Hard phase forming alloy powder, wear resistant sintered alloy, and production method for wear resistant sintered alloy

ABSTRACT

A hard phase forming alloy powder, for forming a hard phase dispersed in a sintered alloy, consists of, by mass %, 15 to 35% of Mo, 1 to 10% of Si, 10 to 40% of Cr, and the balance of Co and inevitable impurities. A production method, for a wear resistant sintered alloy, includes preparing a matrix forming powder, the hard phase forming alloy powder, and a graphite powder. The production method further includes mixing 15 to 45% of the hard phase forming alloy powder and 0.5 to 1.5% of the graphite powder with the matrix forming powder into a raw powder. The production method further includes compacting the raw powder into a green compact having a predetermined shape and includes sintering the green compact. A wear resistant sintered alloy exhibits a metallic structure in which 15 to 45% of a hard phase is dispersed in a matrix. The hard phase consists of, by mass %, 15 to 35% of Mo, 1 to 10% of Si, 10 to 40% of Cr, and the balance of Co and inevitable impurities.

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention relates to a hard phase forming alloy powder thatmay preferably be used for forming a hard phase dispersed in a wearresistant sintered alloy. The wear resistant sintered alloy, such asthat used in valve sheets for internal-combustion engines, must havewear resistance at high temperatures. The present invention also relatesto a production method for a wear resistant sintered alloy using thehard phase forming alloy powder, and the wear resistant sintered alloymay preferably be used for valve sheets for internal-combustion engines.In addition, the present invention relates to a wear resistant sinteredalloy obtained by the production method.

2. Background Art

For a sintered alloy, the alloy design can be freely selected, andvarious characteristics, such as heat resistance and wear resistance,can be easily added thereto compared to doing so for ingot materials.Therefore, the sintered alloy is used for valve sheets forinternal-combustion engines. In such wear resistant sintered alloy forvalve sheets, a hard phase having a high degree of hardness is generallydispersed in an iron-based alloy matrix primarily to improve wearresistance. For example, the following sintered alloys are known. Asintered alloy, in which ferroalloy particles are dispersed in aniron-based alloy matrix as a hard phase, is disclosed in Japanese PatentApplication of Laid-Open No. 64-015349. This sintered alloy is formed byadding a ferroalloy powder, such as ferromolybdenum and ferrotungsten,to a raw powder and then sintering. Another sintered alloy, in which ahard phase is dispersed in an iron-based alloy matrix, is disclosed inJapanese Patent Application of Laid-Open No. 09-195012. This sinteredalloy is formed by adding a high-speed tool steel powder or a die steelpowder to a raw powder and then sintering, and metal carbides aredispersed in the hard phase. Specifically, when high wear resistance isrequired for a sintered alloy, it is preferable that a Co-based alloypowder or a Ni-based alloy powder (see Japanese Patent Application ofLaid-Open No. 10-046298) be added to a raw powder and be dispersed as ahard phase. For the Co-based alloy powder, a Co—Cr—W alloy (see JapanesePatent Application of Laid-Open No. 64-015349) and a Co—Mo—Si alloy (seeJapanese Patent Application of Laid-Open No. 56-152947) may be used.

SUMMARY OF THE INVENTION

The cost of a wear resistant sintered alloy, in which Co—Mo—Si alloy isdispersed as a hard phase, has increased because the costs of Co and Mohave been rising recently. In view of recent environmental issues andcrude oil depletion issue, alcohol-based fuels of biological origin(biofuels) are being used more frequently as fuels forinternal-combustion engines. The alcohol fuels generate acidic materialsduring combustion, and therefore, a wear resistant sintered alloy usedfor valve sheets is required to have higher corrosion resistance.Accordingly, an object of the present invention is to provide a hardphase forming alloy powder at lower cost, and the hard phase formingalloy powder exhibits wear resistance to the same degree or to a greaterdegree than the degree of wear resistance obtained by using aconventional Co—Mo—Si alloy powder. Moreover, an object of the presentinvention is to provide a wear resistant sintered alloy at lower cost,and the wear resistant sintered alloy has higher corrosion resistancethan the corrosion resistance of a conventional sintered alloy.Furthermore, an object of the present invention is to provide aproduction method for the wear resistant sintered alloy. In thefollowing description, all of the symbols “%” represent percentages ofmass ratio, that is, “mass %”.

The present invention provides a hard phase forming alloy powder forforming a hard phase dispersed in a sintered alloy. The hard phaseforming alloy powder consists of, by mass %, 15 to 35% of Mo, 1 to 10%of Si, 10 to 40% of Cr (preferably, 20 to 40% of Cr), and the balance ofCo and inevitable impurities. In this case, not more than 80 mass % ofCo is preferably substituted by Fe, and not more than 5 mass % of Mn ispreferably added.

In the hard phase forming alloy powder of the present invention, Cr,which is relatively low cost, is used as a matrix strengthening element.Cr is added to a raw powder of a wear resistant sintered alloy and issintered, whereby Cr forms a hard phase dispersed in the sintered alloy.In sintering, Cr in the hard phase forming alloy powder strengthens thealloy matrix of the hard phase, and Cr is dispersed from the hard phaseforming alloy powder and strengthens the iron-based alloy matrix of thewear resistant sintered alloy. In addition, Cr forms a passive oxidefilm on the surface of a wear resistant part. Therefore, a wearresistant sintered alloy using the hard phase forming alloy powder ofthe present invention exhibits superior corrosion resistance and wearresistance.

The present invention provides a production method for a wear resistantsintered alloy, and the production method includes mixing 15 to 45% ofthe hard phase forming alloy powder and 0.5 to 1.5% of a graphite powderwith a matrix forming powder into a raw powder. The production methodfurther includes compacting the raw powder into a green compact having apredetermined shape and includes sintering the green compact.

In the production method for the wear resistant sintered alloy,according to a first aspect of the present invention, the matrix formingpowder is preferably made of a mixed powder consisting of 1 to 5 mass %of a nickel powder and the balance of an iron powder. As the ironpowder, an ore-reduced iron powder including 0.3 to 1.5 mass % of metaloxides is more preferably used.

In the production method for the wear resistant sintered alloy,according to a second aspect of the present invention, the matrixforming powder is preferably made of an iron alloy powder consisting of1 to 5 mass % of Cr and the balance of Fe and inevitable impurities. Inthis case, the iron alloy powder preferably includes at least one of Mo,V, and Nb at not more than 2.4 mass %. In the second aspect of thepresent invention, the matrix forming powder is more preferably made ofa mixed powder consisting of the iron alloy powder and not more than 5mass % of a nickel powder with respect to the raw powder.

In the production method for the wear resistant sintered alloy,according to a third aspect of the present invention, the matrix formingpowder is preferably made of an iron alloy powder consisting of, by mass%, 3 to 8% of Co, 1 to 2% of Ni, 1 to 2% of Mo, and the balance of Feand inevitable impurities. In the third aspect of the present invention,the matrix forming powder is more preferably made of a mixed powderconsisting of the iron alloy powder and not more than 5 mass % of anickel powder with respect to the raw powder.

In the production method for the wear resistant sintered alloy,according to a fourth aspect of the present invention, the matrixforming powder is preferably made of an iron alloy powder consisting of,by mass %, 1 to 3% of Ni, 0.5 to 2% of Mo, 0.1 to 1% of Cr, 0.1 to 0.5%of Mn, and the balance of Fe and inevitable impurities. In the fourthaspect of the present invention, the matrix forming powder is morepreferably made of a mixed powder consisting of the iron alloy powderand not more than 5 mass % of at least one of a nickel powder and acopper powder with respect to the raw powder.

In the production method for the wear resistant sintered alloy,according to a fifth aspect of the present invention, the matrix formingpowder is preferably made of an iron alloy powder consisting of 1 to 7mass % of Mo and the balance of Fe and inevitable impurities. In thefifth aspect of the present invention, the matrix forming powder is morepreferably made of a mixed powder consisting of the iron alloy powderand not more than 5 mass % of a nickel powder with respect to the rawpowder.

In the production method for the wear resistant sintered alloy of thepresent invention, at least one kind of powder of a machinabilityimproving material is preferably added to the raw powder at 0.3 to 2mass %. The powder of the machinability improving material is selectedfrom the group consisting of lead powder, disulfide molybdenum powder,manganese sulfide powder, boron nitride powder, calcium metasilicatemineral powder, and calcium fluoride powder. The wear resistant sinteredalloy obtained by sintering has pores, and one selected from the groupconsisting of lead, lead alloy, copper, copper alloy, and acrylic resinis preferably infiltrated or impregnated into the pores.

The present invention provides a wear resistant sintered alloy having ametallic structure in which 15 to 45% of a hard phase is dispersed inthe matrix, and the hard phase consists of 15 to 35% of Mo, 1 to 10% ofSi, 10 to 40% of Cr, and the balance of Co and inevitable impurities. Inthe composition of the hard phase, not more than 80 mass % of Co ispreferably substituted by Fe, and not more than 5 mass % of Mn ispreferably added.

In the wear resistant sintered alloy, according to a first aspect of thepresent invention, the overall composition preferably consists of, bymass %, 1 to 5% of Ni, 2.25 to 33.3% of Co, 1.5 to 18% of Cr, 2.25 to15.75% of Mo, 0.15 to 4.5% of Si, 0.5 to 1.5% of C, and the balance ofFe and inevitable impurities. In this case, the matrix is preferablymade of an Fe—Ni—C alloy. In addition, at least one kind of an oxide ofa metal is more preferably added in the Fe—Ni—C alloy matrix at 0.15 to1.25 mass % with respect to the overall composition. The metal isselected from the group consisting of aluminum, silicon, magnesium,iron, titanium, and calcium.

In the wear resistant sintered alloy, according to a second aspect ofthe present invention, the overall composition preferably consists of,by mass %, 2.34 to 20.73% of Cr, 2.25 to 15.75% of Mo, 0.15 to 4.5% ofSi, 2.25 to 33.3% of Co, 0.5 to 1.5% of C, and the balance of Fe andinevitable impurities. In this case, the matrix is preferably made of anFe—Cr—C alloy. In addition, more preferably, at least one of Mo, V, andNb is added in the Fe—Cr—C alloy matrix at not more than 2 mass % withrespect to the overall composition. Moreover, Ni is more preferablyadded in the Fe—Cr—C alloy matrix at not more than 5 mass % with respectto the overall composition.

In the wear resistant sintered alloy, according to a third aspect of thepresent invention, the overall composition preferably consists of, bymass %, 1.5 to 18% of Cr, 0.54 to 1.69% of Ni, 3.09 to 16.84% of Mo,0.15 to 4.5% of Si, 4.76 to 37.66% of Co, 0.5 to 1.5% of C, and thebalance of Fe and inevitable impurities. In this case, the matrix ispreferably made of an Fe—Co—C alloy. In addition, Ni is more preferablyadded in the Fe—Co—C alloy matrix at not more than 5 mass % with respectto the overall composition.

In the wear resistant sintered alloy, according to a fourth aspect ofthe present invention, the overall composition preferably consists of,by mass %, 1.58 to 18.55% of Cr, 0.54 to 2.54% of Ni, 2.67 to 16.84% ofMo, 0.15 to 4.5% of Si, 2.25 to 33.30% of Co, 0.05 to 0.42% of Mn, 0.5to 1.5% of C, and the balance of Fe and inevitable impurities. In thiscase, the matrix is preferably made of an Fe—Ni—Mo—C alloy. In addition,at least one of Ni and Cu is more preferably added in the Fe—Ni—Mo—Calloy matrix at not more than 5.0 mass % with respect to the overallcomposition.

In the wear resistant sintered alloy, according to a fifth aspect of thepresent invention, the overall composition preferably consists of, bymass %, 1.5 to 18% of Cr, 3.09 to 19.57% of Mo, 0.15 to 4.5% of Si, 2.25to 33.3% of Co, 0.5 to 1.5% of C, and the balance of Fe and inevitableimpurities. In this case, the matrix is preferably made of an Fe—Mo—Calloy. In addition, Ni is more preferably added in the Fe—Mo—C alloymatrix at not more than 5.0 mass % with respect to the overallcomposition.

In the wear resistant sintered alloy of the present invention, thesintered alloy has pores and grain boundaries, and 0.3 to 2 mass % of atleast one kind of powder of machinability improving material ispreferably dispersed in the pores and the grain boundaries. Themachinability improving material is selected from the group consistingof lead, disulfide molybdenum, manganese sulfide, boron nitride, calciummetasilicate mineral, and calcium fluoride. In addition, one selectedfrom the group consisting of lead, lead alloy, copper, copper alloy, andacrylic resin is preferably infiltrated or impregnated in the pores ofthe sintered alloy.

In the hard phase forming alloy powder of the present invention, Cr,which is relatively low cost, is used as a matrix strengthening element.Cr is added to the raw powder of a wear resistant sintered alloy and issintered, whereby Cr forms a hard phase dispersed in the sintered alloy.In sintering, Cr in the hard phase forming alloy powder strengthens thealloy matrix of the hard phase, and Cr is dispersed from the hard phaseforming alloy powder and strengthens the iron based alloy matrix of thewear resistant sintered alloy. In addition, Cr forms a passive oxidefilm on the surface of a wear resistant part. Therefore, the wearresistant sintered alloy using the hard phase forming alloy powder ofthe present invention exhibits superior corrosion resistance and wearresistance. Accordingly, the wear resistant sintered alloy of thepresent invention is preferably used for valve sheets ofinternal-combustion engines using an alcohol fuel as a fuel.

PREFERRED EMBODIMENTS OF THE INVENTION 1. Hard Phase Forming AlloyPowder

Similar to a conventional Co—Mo—Si alloy powder, the hard phase formingalloy powder of the present invention is added to a raw powder and issintered, whereby the hard phase forming alloy powder is dispersed inthe matrix as a hard phase. The essential feature of the presentinvention is that a great amount of Cr is added to the conventionalCo—Mo—Si alloy powder so as to improve the conventional Co—Mo—Si alloypowder.

Co is included in the hard phase forming alloy powder of the presentinvention and is solid-solved in the alloy matrix of the hard phaseformed by the hard phase forming alloy powder. As a result, Co improvesheat resistance of the hard phase and also improves strength and wearresistance at high temperatures. Co included in the hard phase formingalloy powder is dispersed in the matrix of a sintered alloy insintering, whereby the matrix of the sintered alloy is strengthened bysolid solution strengthening, and the hard phase is strongly combined tothe matrix of the sintered alloy. In addition, a partial amount of Cocombines with Mo, Cr, and Si and forms molybdenum silicides, chromiumsilicides, and complex silicides thereof. The silicides function as acore of a hard phase and prevent plastic flow and adhesion of the matrixof the sintered alloy, whereby wear resistance is improved.

Mo is included in the hard phase forming alloy powder of the presentinvention and is dispersed in the matrix of a sintered alloy insintering. As a result, the matrix of the sintered alloy is strengthenedby solid solution strengthening, and quenchability of the matrix of thesintered alloy is improved, whereby strength and wear resistance of thesintered alloy are improved. Mo combines mainly with Si and forms hardmolybdenum silicides, and a partial amount of Mo reacts with Cr and Coand forms complex silicides. The silicides function as a core of thehard phase. Therefore, plastic flow and adhesion of the matrix of thesintered alloy are prevented, whereby wear resistance is improved. Inthis case, when the amount of Mo in the hard phase forming alloy powderis less than 15%, the matrix is not sufficiently strengthened. Moreover,silicides are not sufficiently precipitated, and the above pinningeffect is not sufficiently obtained, whereby wear resistance isdecreased. On the other hand, when more than 35% of Mo is included inthe hard phase forming alloy powder, the hard phase forming alloy powderis hardened, whereby compressibility of the raw powder is decreased.Moreover, since the amount of silicides is increased, a mating part maybe easily worn. Therefore, the amount of Mo in the hard phase formingalloy powder is set to be 15 to 35%.

Si combines with Mo, Co, and Cr and forms hard molybdenum silicides,chromium silicides, and complex silicides thereof, thereby improvingwear resistance. When the amount of Si in the hard phase forming alloypowder is less than 1%, silicides are not sufficiently precipitated.When the amount of Si in the hard phase forming alloy powder is greaterthan 10%, the hard phase forming alloy powder is hardened, wherebycompressibility and sinterability is decreased. Therefore, the amount ofSi in the hard phase forming alloy powder is set to be 1 to 10%.

Cr is solid-solved in the alloy matrix of the hard phase that is formedafter sintering, whereby the alloy matrix of the hard phase isstrengthened. Moreover, Cr is dispersed in the matrix of a sinteredalloy in sintering and strengthens the matrix of the sintered alloy. Crdispersed in the sintered alloy forms a passive oxide film on thesurface of a wear resistant part and improves corrosion resistance andoxidation resistance. A partial amount of Cr combines with Si, Mo, andCo and forms hard chromium silicides and complex silicides. Cr is low incost compared to the costs of Co and Mo, and Cr is added to decrease theamount of Co, whereby the hard phase forming alloy powder isinexpensive, and a wear resistant sintered alloy can be produced atlower cost. When Cr having the above effects in the hard phase formingalloy powder is less than 10%, the above effects are not sufficientlyobtained. In order to efficiently obtain the above effects, the amountof Cr is preferably set to be 20% or more. On the other hand, when theamount of Cr in the hard phase forming alloy powder is greater than 40%,oxide films are strongly formed on the surfaces of the hard phaseforming alloy powder particles, whereby sintering may be prevented.Moreover, since the hard phase forming alloy powder is hardened by theoxide films, compressibility of the raw powder is decreased, andstrength and wear resistance of the sintered alloy are decreased.Therefore, the amount of Cr in the hard phase forming alloy powder isset to be 10 to 40%, preferably, 20 to 40%.

In the present invention, by setting the amount of Cr in the hard phaseforming alloy powder for forming a hard phase as described above,corrosion resistance and oxidation resistance are improved. Therefore, apartial amount of Co for forming the alloy matrix of the hard phase canbe substituted by Fe. That is, since Cr solid-solved in Fe forms apassive oxide film and thereby improves corrosion resistance andoxidation resistance, Fe, which is inexpensive, can be substituted partof the amount of Co that has superior corrosion resistance but isexpensive. In this case, not more than 80% of Co in the hard phaseforming alloy powder can be substituted by Fe.

In the present invention, by adding Mn in the hard phase forming alloypowder, Mn is solid-solved in the alloy matrix of the hard phase formedafter sintering, and the alloy matrix of the hard phase is strengthened.By strengthening the alloy matrix of the hard phase in this manner, flowand drop off of silicides (molybdenum silicides, chromium silicides, andcomplex silicides thereof) precipitated in the hard phase are prevented,whereby superior wear resistance is obtained under severe conditions. Mnis dispersed in Fe matrix of the sintered alloy and increases fixabilityof the hard phase, whereby drop off of the hard phase is prevented, andwear resistance is improved. When the amount of such Mn in the hardphase forming alloy powder is greater than 5%, Mn oxide films are formedon the surface layers of the hard phase forming alloy powder particles,whereby dispersion during sintering is prevented, and the fixability ofthe hard phase is decreased. Therefore, the upper limit of the amount ofMn in the hard phase forming alloy powder is set to be 5%.

For the matrix of the wear resistant sintered alloy, in which the hardphase made from the hard phase forming alloy powder of the presentinvention is dispersed, a conventional wear resistant sintered alloymatrix may be used, and specifically, a low-alloy steel or a stainlesssteel may be used. That is, in a raw powder of a sintered alloy to whicha conventional Co—Mo—Si based hard phase forming alloy powder is added,instead of using the conventional Co—Mo—Si based hard phase formingalloy powder, the hard phase forming alloy powder of the presentinvention can be used. When such a raw powder is compacted and issintered, a sintered alloy is obtained. This sintered alloy hascorrosion resistance, oxidation resistance, and wear resistance to thesame degree or to degrees greater than those of a wear resistantsintered alloy in which a hard phase made from a conventional Co—Mo—Sibased hard phase forming alloy powder is dispersed. In addition, sincethe amount of Co that is expensive is decreased, the sintered alloy canbe produced at lower cost.

2. Production Method for Wear Resistant Sintered Alloy and WearResistant Sintered Alloy 2-1. Basic Formation

In the present invention, Cr is dispersed in the matrix and forms apassive oxide film by using the above hard phase, and corrosionresistance of the matrix is improved. Therefore, the matrix can be madeof an iron alloy, which is relatively inexpensive, without using largeamounts of Co and Mo, which are expensive. Specifically, a wearresistant sintered alloy is obtained by the following method. The abovehard phase forming alloy powder and a graphite powder are mixed with aniron based matrix forming powder into a raw powder. Then, the raw powderis compacted into a green compact having a predetermined shape, and thegreen compact is sintered.

When the hard phase forming alloy powder is added to the raw powder atless than 15%, wear resistance is not sufficiently obtained. The hardphase forming alloy powder of the present invention is made byincreasing the amount of Cr in a conventional Co—Mo—Si based hard phaseforming alloy powder. Since Cr is solid-solved in the Co-alloy matrix,the hardness of the hard phase forming alloy powder is increased, andcompressibility thereof is decreased. Therefore, when the hard phaseforming alloy powder is added to the raw powder at more than 45%, thecompressibility of the raw powder is greatly decreased. Accordingly, thehard phase forming alloy powder is added to the raw powder at 15 to 45%.

The hard phase dispersed in the matrix of the wear resistant sinteredalloy is formed by adding the hard phase forming alloy powder and agraphite powder to the iron based matrix forming powder and bysintering. Since the hard phase forming alloy powder is added to the rawpowder at 15 to 45%, the amount of the hard phase dispersed in thematrix of the wear resistant sintered alloy is 15 to 45%. As describedabove, the hard phase forming alloy powder consists of 15 to 35% of Mo,1 to 10% of Si, 10 to 40% of Cr, and the balance of Co and inevitableimpurities. Therefore, in the overall composition of the wear resistantsintered alloy, the amount of Co is 2.25 to 33.3%, the amount of Cr is1.5 to 18%, the amount of Mo is 2.25 to 15.75%, and the amount of Si is0.15 to 4.5%. When Mn is added to the hard phase forming alloy powder,the amount of Mn in the overall composition is not more than 2.25%.

A graphite powder is added as a source of C. C is dispersed in the ironbased matrix forming powder in sintering and is solid-solved in the Fematrix, whereby the Fe matrix is strengthened. Moreover, C is added inorder to form a matrix structure made of martensite or bainite, whichhave high strength. When the amount of C is less than 0.5%, the aboveeffects are not sufficiently obtained. On the other hand, when theamount of C is greater than 1.5%, brittle cementite may be precipitatedat grain boundaries, whereby strength and wear resistance of the wearresistant sintered alloy are decreased. Therefore, the amount of C inthe overall composition is set to be 0.5 to 1.5%. If such C is added andis solid-solved in the iron powder, the hardness of the iron powder isincreased, and the compressibility is greatly decreased. Therefore, theentire amount of C is added in the form of a graphite powder.Accordingly, a graphite powder is added to the matrix forming powder at0.5 to 1.5%.

In the production method for the wear resistant sintered alloy of thepresent invention, the raw powder is compacted into a green compacthaving a predetermined shape, and the green compact is sintered. Thecompacting and the sintering may be performed in the same manner asthose for a conventional wear resistant sintered alloy using a Co—Mo—Sialloy powder as a hard phase forming alloy powder. That is, thecompacting may be performed at a compacting pressure of 600 to 1000 MPa,and the sintering may be performed at a sintering temperature of 1000 to1300° C.

A sintered alloy obtained by the above production method exhibits ametallic structure in which 15 to 45% of a hard phase is dispersed in amatrix, and the hard phase consists of 15 to 35% of Mo, 1 to 10% of Si,10 to 40% of Cr, and the balance of Co and inevitable impurities.

In the wear resistant sintered alloy of the present invention, amachinability improving technique that is conventionally performed maybe used. That is, at least one kind of machinability improving materialmay be added to the raw powder at 0.3 to 2% so as to disperse themachinability improving material in the pores and grain boundaries ofthe wear resistant sintered alloy. The machinability improving materialis selected from the group consisting of lead powder, disulfidemolybdenum powder, manganese sulfide powder, boron nitride powder,calcium metasilicate mineral powder, and calcium fluoride powder. Thesematerials are machinability improving components, and the materialsfunction as a starting point for breaking during machining when thematerials are dispersed in the matrix, whereby the machinability of thesintered alloy is improved. When the amount of the machinabilityimproving components is less than 0.3%, the effects are not sufficientlyobtained. On the other hand, when the amount of the machinabilityimproving components is greater than 2%, the strength of the sinteredalloy is decreased.

One selected from the group consisting of lead, lead alloy, copper,copper alloy, and acrylic resin may be infiltrated or impregnated in thepores of the wear resistant sintered alloy of the present invention.When a sintered alloy having pores is machined, the machining isintermittently performed, and impact is intermittently applied to anedge of a tool. However, by adding lead, copper, and the like in thepores, the machining may be continuously performed, and the degree ofimpact at an edge of a tool is decreased. Lead and lead alloy functionas a solid lubricant. Copper and copper alloy have high thermalconductivity, thereby preventing thermal accumulation and decreasingthermal damages at the edge. Acrylic resin functions as a starting pointfor breaking in machining.

2-2. Fe—Ni—C Alloy Matrix

In the above wear resistant sintered alloy, according to the firstpreferred embodiment of the present invention, the matrix of the wearresistant sintered alloy is made of an Fe—Ni—C alloy. The Fe—Ni—C alloydoes not include Co and Mo, which are expensive, whereby a wearresistant sintered alloy may be formed at lower cost.

Ni is solid-solved in the Fe matrix and thereby strengthens the Fematrix, and Ni is added in order to easily obtain martensite at acooling rate after sintering. Ni having such effects is dispersed in. Feat relatively high rate during sintering. Moreover, if Ni is added inthe form of an Fe—Ni alloy powder in which Ni is solid-solved in Fe, themain raw powder is hardened. Therefore, Ni is added by adding a nickelpowder to the iron powder. In this case, when the nickel powder is addedto the iron powder at less than 1%, the above effects are notsufficiently obtained. On the other hand, when the nickel powder isadded to the iron powder at more than 5%, a large amount of Ni-richaustenite having low wear resistance is formed and remains. Therefore,the nickel powder is added to the iron powder at 1 to 5%.

C is solid-solved in the Fe matrix and thereby strengthens the Fematrix, and C is added in order to form a matrix structure made ofmartensite or bainite, which have high strength. When the amount of C isless than 0.5%, the above effects are not sufficiently obtained. On theother hand, when the amount of C is greater than 1.5%, brittle cementitemay be precipitated at grain boundaries, whereby strength and wearresistance of the wear resistant sintered alloy are decreased.Therefore, the amount of C in the overall composition is set to be 0.5to 1.5%. If such C is added and is solid-solved in the iron powder, thehardness of the iron powder is increased, and the compressibility isgreatly decreased. Accordingly, the entire amount of C is added in theform of a graphite powder.

As described above, according to the first embodiment of the presentinvention, the production method for the wear resistant sintered alloyincludes preparing an iron powder, a nickel powder, a hard phase formingalloy powder, and a graphite powder. The hard phase forming alloy powderconsists of, by mass %, 15 to 35% of Mo, 1 to 10% of Si, 10 to 40% ofCr, and the balance of Co and inevitable impurities. The productionmethod further includes mixing 1 to 5% of the nickel powder, 15 to 45%of the hard phase forming alloy powder, and 0.5 to 1.5% of the graphitepowder with the iron powder into a raw powder. The production methodfurther includes compacting the raw powder into a green compact having apredetermined shape and includes sintering the green compact.

As described above, according to the first embodiment of the presentinvention, the wear resistant sintered alloy consists of, by mass %, 1to 5% of Ni, 2.25 to 33.3% of Co, 1.5 to 18% of Cr, 2.25 to 15.75% ofMo, 0.15 to 4.5% of Si, 0.5 to 1.5% of C, and the balance of Fe andinevitable impurities. The wear resistant sintered alloy exhibits ametallic structure in which 15 to 45% of a hard phase is dispersed in anFe—Ni—C alloy matrix, and the hard phase consists of 15 to 35% of Mo, 1to 10% of Si, 10 to 40% of Cr, and the balance of Co and inevitableimpurities.

The matrix of the wear resistant sintered alloy of the present inventionis made of an Fe—Ni—C alloy by adding a nickel powder and a graphitepowder to the iron powder, as described above. In this case, as the ironpowder of the main raw material, an ore-reduced iron powder ispreferably used. The ore-reduced iron powder includes a very smallamount of metallic oxides, such as aluminum, silicon, magnesium, iron,titanium, and calcium, due to the production method thereof. Thesemetallic oxides are dispersed in the matrix as fine metallic oxidephases, and these metallic oxides function as free-machining componentsand improve machinability. In contrast, an atomized iron powder and amill scale-reduced iron powder, which are generally used, do not includesufficient amount of metallic oxides, and the above effect for improvingmachinability is not obtained therefrom. In order to obtain the effectfor improving the machinability, at least one kind of metallic oxides isrequired at 0.3% or more, and the metallic oxide is selected from thegroup consisting of aluminum, silicon, magnesium, iron, titanium, andcalcium. On the other hand, when the amount of the metallic oxides inthe ore-reduced iron powder is greater than 1.5%, the matrix isembrittled, and the compressibility of the iron powder is decreased.Therefore, the amount of the metallic oxides in the ore-reduced ironpowder is set to be 0.3 to 1.5%. This amount of the metallic oxidescorresponds to 0.15 to 1.25% with respect to the overall composition.

2-3. Fe—Cr—C Alloy Matrix

In the above wear resistant sintered alloy, according to the secondpreferred embodiment of the present invention, the matrix of the wearresistant sintered alloy is made of an Fe—Cr—C alloy. The Fe—Cr—C alloydoes not include Co and Mo, which are expensive, whereby a wearresistant sintered alloy may be formed at lower cost. By preliminarilyadding Cr to the matrix, corrosion resistance of the matrix is furtherimproved. Since Cr is dispersed from the above hard phase to the matrix,the amount of Cr in the Fe—Cr—C alloy matrix can be small compared tothe amount of Cr in the hard phase.

Cr included in the matrix forms a passive oxide film and therebyimproves the corrosion resistance of the matrix, and Cr is solid-solvedin the Fe matrix and strengthens the Fe matrix. Moreover, Cr included inthe matrix improves the quenchability of the matrix and forms a matrixstructure made of a bainite structure having high strength and hightoughness at a cooling rate after sintering. In order to uniformly addsuch effects of Cr to the entirety of the matrix, Cr is alloyed with Feand is added in the form of the iron alloy powder. In this case, whenthe amount of Cr in the iron alloy powder is less than 1%, the aboveeffects are not sufficiently obtained. On the other hand, when theamount of Cr in the iron alloy powder is greater than 5%, the hardnessof the iron alloy powder is increased, and the compressibility of theraw powder is decreased. Therefore, the amount of Cr in the iron alloypowder is set to be 1 to 5%.

C is solid-solved in the Fe matrix and thereby strengthens the Fematrix, and C is added in order to form a matrix structure made ofmartensite or bainite having high strength. When the amount of C is lessthan 0.5%, the above effects are not sufficiently obtained. On the otherhand, when the amount of C is greater than 1.5%, C combines with Cr andprecipitates Cr carbides in the matrix. Cr was added to form a passiveoxide film and to improve the corrosion resistance of the matrix. As aresult, the concentration of Cr in the matrix is decreased, and thecorrosion resistance of the matrix is decreased. Therefore, the amountof C in the overall composition is set to be 0.5 to 1.5%. If such C isadded and is solid-solved in the above iron alloy powder, the hardnessof the iron alloy powder is increased, and the compressibility of theraw powder is greatly decreased. Accordingly, the entire amount of C isadded in the form of a graphite powder.

As described above, according to the second embodiment of the presentinvention, the production method for the wear resistant sintered alloyincludes preparing an iron alloy powder, a hard phase forming alloypowder, and a graphite powder. The iron alloy powder consists of, bymass %, 1 to 5% of Cr and the balance of Fe and inevitable impurities.The hard phase forming alloy powder consists of, by mass %, 15 to 35% ofMo, 1 to 10% of Si, 10 to 40% of Cr, and the balance of Co andinevitable impurities. The production method further includes mixing 15to 45% of the hard phase forming alloy powder and 0.5 to 1.5% of thegraphite powder with the iron alloy powder into a raw powder. Theproduction method further includes compacting the raw powder into agreen compact having a predetermined shape and includes sintering thegreen compact.

As described above, according to the second embodiment of the presentinvention, the wear resistant sintered alloy consists of, by mass %,2.34 to 20.73% of Cr, 2.25 to 15.75% of Mo, 0.15 to 4.5% of Si, 2.25 to33.3% of Co, 0.5 to 1.5% of C, and the balance of Fe and inevitableimpurities. The wear resistant sintered alloy exhibits a metallicstructure in which 15 to 45% of a hard phase is dispersed in an Fe—Cr—Calloy matrix, and the hard phase consists of 15 to 35% of Mo, 1 to 10%of Si, 10 to 40% of Cr, and the balance of Co and inevitable impurities.

Mo, V, and Nb have higher carbide-forming ability than that of Cr.Therefore, in the wear resistant sintered alloy having the above Fe—Cr—Calloy matrix of the present invention, by adding at least one of Mo, V,and Nb to the Fe—Cr—C alloy matrix, Mo, V, and Nb selectively combinewith the above C and form fine metallic carbides dispersed in thematrix. Accordingly, corrosion resistance is not decreased by theprecipitation of Cr carbides. In addition, mechanical strength and wearresistance of the matrix can be improved. In order to uniformly addthese effects to the entirety of the matrix, at least one of Mo, V, andNb is preferably added and is solid-solved in the iron alloy powder. Inthis case, when more than 2.4% of Mo, V, and Nb are added to the ironalloy powder, the hardness of the iron alloy powder is increased, andthe compressibility of the raw powder is decreased. Therefore, the totalamount of Mo, V, and Nb added to the iron alloy powder is set to be notmore than 2.4%. This total amount of Mo, V, and Nb corresponds to notmore than 2 mass % with respect to the overall composition.

Ni is solid-solved in the Fe matrix and thereby strengthens the Fematrix, and Ni improves the quenchability of the matrix. Therefore, in acase of improving wear resistance and mechanical strength by forming amatrix structure made of a martensite structure or a mixed structure ofa martensite structure and a bainite structure, instead of forming amatrix structure made of a bainite structure, Ni is added. Ni havingsuch effects is dispersed into Fe at relatively high rate in sintering.Moreover, if Ni is added and is solid-solved in the above iron alloypowder, the iron alloy powder is hardened, and the compressibility ofthe main raw powder is decreased. Therefore, Ni is added by adding anickel powder to the iron alloy powder. In this case, when the nickelpowder is added to the raw powder at more than 5%, a large amount ofNi-rich austenite having low wear resistance is formed and remains inthe matrix. Therefore, the upper limit of the amount of the nickelpowder added to the raw powder is set to be 5%.

2-4. Fe—Co—C Alloy Matrix

In the above wear resistant sintered alloy, according to the thirdembodiment of the present invention, the matrix of the wear resistantsintered alloy is made of an Fe—Co—C alloy. The Fe—Co—C alloy includesCo and Mo, but the amounts of Co and Mo are small, whereby a wearresistant sintered alloy can be formed at lower cost than the cost of aconventional wear resistant sintered alloy.

Co is solid-solved in the Fe matrix and thereby strengthens the Fematrix, and Co increases the heat resistance of the matrix and improvesthe wear resistance at high temperatures. In order to uniformly add sucheffects of Co to the entirety of the matrix, Co is alloyed with Fe andis added in the form of an iron alloy powder. In this case, when theamount of Co in the iron alloy powder is less than 3%, the above effectsare not sufficiently obtained. On the other hand, when the amount of Coin the iron alloy powder is greater than 8%, the hardness of the ironalloy powder is increased, the compressibility of the raw powder isdecreased, and the cost of the iron alloy powder is high. Therefore, theamount of Co in the iron alloy powder is set to be 3 to 8%.

Mo is solid-solved in the Fe matrix and thereby strengthens the Fematrix, and Mo increases the quenchability of the matrix and improvesthe strength and wear resistance of the matrix. In order to uniformlyadd such effects of Mo to the entirety of the matrix, Mo is added bysolid solving Mo in the above iron alloy powder. In this case, when theamount of Mo in the iron alloy powder is less than 1%, the above effectsare not sufficiently obtained. On the other hand, when the amount of Moin the iron alloy powder is greater than 2%, the above improving effectsare not efficiently obtained, and the hardness of the iron alloy powderis increased, thereby decreasing the compressibility of the raw powder.Therefore, the amount of Mo in the iron alloy powder is set to be 1 to2%.

Ni is solid-solved in the Fe matrix and thereby strengthens the Fematrix, and Ni increases the quenchability of the matrix and improvesthe strength and wear resistance of the matrix. In order to uniformlyadd such effects of Ni to the entirety of the matrix, Ni is added bysolid solving Ni in the above iron alloy powder. In this case, when theamount of Ni in the iron alloy powder is less than 1%, the above effectsare not sufficiently obtained. On the other hand, when the amount of Niin the iron alloy powder is greater than 2%, the hardness of the ironalloy powder is increased, and the compressibility of the raw powder isdecreased. Therefore, the amount of Ni in the iron alloy powder is setto be 1 to 2%.

C is solid-solved in the Fe matrix and strengthens the Fe matrix, and Cis added in order to form a matrix structure made of martensite orbainite having high strength. When the amount of C is less than 0.5%,the above effects are not sufficiently obtained. On the other hand, whenthe amount of C is greater than 1.5%, C combines with Cr andprecipitates Cr carbides in the matrix. Cr was added for forming apassive oxide film and improving corrosion resistance of the matrix. Asa result, the concentration of Cr in the matrix is decreased, and thecorrosion resistance of the matrix is decreased. Therefore, the amountof C in the overall composition is set to be 0.5 to 1.5%. If such C isadded and is solid-solved in the above iron alloy powder, the hardnessof the iron alloy powder is increased, and the compressibility of theraw powder is greatly decreased. Accordingly, the entire amount of C isadded in the form of a graphite powder.

As described above, according to the third embodiment of the presentinvention, the production method of the wear resistant sintered alloyincludes preparing an iron alloy powder, a hard phase forming alloypowder, and a graphite powder. The iron alloy powder consists of, bymass %, 3 to 8% of Co, 1 to 2% of Ni, 1 to 2% of Mo, and the balance ofFe and inevitable impurities. The hard phase forming alloy powderconsists of, by mass %, 15 to 35% of Mo, 1 to 10% of Si, 10 to 40% ofCr, and the balance of Co and inevitable impurities. The productionmethod further includes mixing 15 to 45% of the hard phase forming alloypowder and 0.5 to 1.5% of the graphite powder with the iron alloy powderinto a raw powder. The production method further includes compacting theraw powder into a green compact having a predetermined shape andincludes sintering the green compact.

As described above, according to the third embodiment of the presentinvention, the wear resistant sintered alloy consists of, by mass %, 1.5to 18% of Cr, 0.54 to 1.69% of Ni, 3.09 to 16.84% of Mo, 0.15 to 4.5% ofSi, 4.76 to 37.66% of Co, 0.5 to 1.5% of C, and the balance of Fe andinevitable impurities. The wear resistant sintered alloy exhibits ametallic structure in which 15 to 45% of a hard phase is dispersed in anFe—Co—C alloy matrix, and the hard phase consists of 15 to 35% of Mo, 1to 10% of Si, 10 to 40% of Cr, and the balance of Co and inevitableimpurities.

In the wear resistant sintered alloy according to the third embodimentof the present invention, if a greater amount of the above effects of Niis required, Ni may be added to the raw powder in the form of a nickelpowder. Since Ni is dispersed into Fe at relatively high rate insintering, Ni is preferably added by alloying. Nevertheless, when alarger amount of Ni is added, Ni may be added in the form of a nickelpowder, because the effects of Ni are easily added to the entirety ofthe matrix compared to the cases of other elements. In this case, whenthe nickel powder is added to the raw powder at greater than 5%, a largeamount of Ni-rich austenite having low wear resistance is formed andremains in the matrix. Therefore, the upper limit of the amount of thenickel powder added to the raw powder is set to be 5%.

2-5. Fe—Ni—Mo—C Alloy Matrix

In the wear resistant sintered alloy, according to the fourth preferredembodiment of the present invention, the matrix of the wear resistantsintered alloy is made of an Fe—Ni—Mo—C alloy. The Fe—Ni—Mo—C alloyincludes Mo, but the amount of Mo is small, and the Fe—Ni—Mo—C alloydoes not include Co. Therefore, a wear resistant sintered alloy can beformed at lower cost than the cost of a conventional wear resistantsintered alloy.

In view of wear resistance, wearing characteristics with respect to amating material, and strength of a wear resistant sintered alloy, themetallic structure of the matrix is made so as to be bainite. In orderto form a matrix structure made of bainite, addition of alloyingelements such as Mo, Ni, and Cr is effective. In order to uniformly addthis effect to the entirety of the matrix structure, these alloyingcomponents are alloyed with Fe and are added in the form of an ironalloy powder. Specifically, the composition of the iron alloy powder isselected so as to consist of, by mass %, 1 to 3% of Ni, 0.5 to 2% of Mo,0.1 to 1% of Cr, 0.1 to 0.5% of Mn, and the balance of Fe and inevitableimpurities. That is, when the amount of Ni is less than 1%, the amountof Mo is less than 0.5%, the amount of Cr is less than 0.1%, and theamount of Mn is less than 0.1%, the matrix is not sufficientlybainitized. On the other hand, when the amount of Ni is greater than 3%,the amount of Mo is greater than 2%, the amount of Cr is greater than1%, and the amount of Mn is greater than 0.5%, the hardness of the alloypowder is increased, and the compressibility is decreased, wherebystrength and wear resistance are decreased.

C is solid-solved in the Fe matrix and thereby strengthens the Fematrix, and C is added in order to form a matrix structure made ofmartensite or bainite having high strength. When the amount of C is lessthan 0.5%, the above effects are not sufficiently obtained. On the otherhand, when the amount of C is greater than 1.5%, C combines with Cr andprecipitates Cr carbides in the matrix. Cr was added for forming apassive oxide film and improving corrosion resistance of the matrix. Asa result, the concentration of Cr in the matrix is decreased, and thecorrosion resistance of the matrix is decreased. Therefore, the amountof C in the overall composition is set to be 0.5 to 1.5%. If such C isadded and is solid-solved in the above iron alloy powder, the hardnessof the iron alloy powder is increased, and the compressibility of theraw powder is greatly decreased. Accordingly, the entire amount of C isadded in the form of a graphite powder.

As described above, according to the fourth embodiment of the presentinvention, the production method of the wear resistant sintered alloyincludes preparing an iron alloy powder, a hard phase forming alloypowder, and a graphite powder. The iron alloy powder consists of, bymass %, 1 to 3% of Ni, 0.5 to 2% of Mo, 0.1 to 1% of Cr, 0.1 to 0.5% ofMn, and the balance of Fe and inevitable impurities. The hard phaseforming alloy powder consists of, by mass %, 15 to 35% of Mo, 1 to 10%of Si, 10 to 40% of Cr, and the balance of Co and inevitable impurities.The production method further includes mixing 15 to 45% of the hardphase forming alloy powder and 0.5 to 1.5% of the graphite powder withthe iron alloy powder into a raw powder. The production method furtherincludes compacting the raw powder into a green compact having apredetermined shape and includes sintering the green compact.

As described above, according to the fourth embodiment of the presentinvention, the wear resistant sintered alloy consists of, by mass %,1.58 to 18.55% of Cr, 0.54 to 2.54% of Ni, 2.67 to 16.84% of Mo, 0.15 to4.5% of Si, 2.25 to 33.30% of Co, 0.05 to 0.42% of Mn, 0.5 to 1.5% of C,and the balance of Fe and inevitable impurities. The wear resistantsintered alloy exhibits a metallic structure in which 15 to 45% of ahard phase is dispersed in an Fe—Ni—Mo—C alloy matrix, and the hardphase consists of 15 to 35% of Mo, 1 to 10% of Si, 10 to 40% of Cr, andthe balance of Co and inevitable impurities.

In the wear resistant sintered alloy according to the fourth embodimentof the present invention, when further improvement of the wearresistance is required, a nickel powder or a copper powder may be addedto the raw powder so as to form a matrix structure which partiallyincludes martensite with high strength and is made of a mixed structureof bainite and martensite. Ni and Cu have great effects for improvingthe quenchability, and a nickel powder and a copper powder have lowhardness. Therefore, by adding a nickel powder or a copper powder to theabove iron alloy powder, a mixed structure of bainite and martensite iseasily formed as a matrix structure. In this case, when the amount ofthe nickel powder added to the iron alloy powder is greater than 5%, alarge amount of Ni-rich austenite having low wear resistance is formedand remains in the matrix. In addition, when the amount of the copperpowder added to the iron alloy powder is greater than 5%, a soft copperphase is precipitated in the matrix, whereby the strength of the matrixis decreased. Therefore, the upper limit of the amount of the nickelpowder added to the iron alloy powder is set to be 5%, and the upperlimit of the copper powder added to the iron alloy powder is set to be5%.

2-6. Fe—Mo—C Alloy Matrix

In the wear resistant sintered alloy, according to the fifth preferredembodiment of the present invention, the matrix of the wear resistantsintered alloy is made of an Fe—Mo—C alloy. The Fe—Mo—C alloy includesMo, but the amount of Mo is small, and the Fe—Ni—Mo—C alloy does notinclude Co. Therefore, a wear resistant sintered alloy can be formed atlower cost than the cost of a conventional wear resistant sinteredalloy.

Mo is solid-solved in the Fe matrix and thereby strengthens the Fematrix, and Mo extends the bainite area of an alloy, whereby Mo forms amatrix structure made of a bainite structure having high strength andhigh toughness at a cooling rate after sintering. In order to uniformlyadd such effects of Mo in the entirety of the matrix, Mo is alloyed withFe and is added in the form of an iron alloy powder. In this case, whenthe amount of Mo in the iron alloy powder is less than 1%, the aboveeffects are not sufficiently obtained. On the other hand, when theamount of Mo in the iron alloy powder is greater than 7%, the hardnessof the iron alloy powder is increased, and the compressibility of theraw powder is decreased. Therefore, the amount of Mo in the iron alloypowder is set to be 1 to 7%.

C is solid-solved in the Fe matrix and thereby strengthens the Fematrix, and C is added in order to form a matrix structure made ofmartensite or bainite having high strength. When the amount of C is lessthan 0.5%, the above effects are not sufficiently obtained. On the otherhand, when the amount of C is greater than 1.5%, brittle cementite maybe precipitated at grain boundaries, whereby strength and wearresistance of the wear resistant sintered alloy are decreased.Therefore, the amount of C in the overall composition is set to be 0.5to 1.5%. If such C is added and is solid-solved in the iron powder, thehardness of the iron powder is increased, and the compressibility isgreatly decreased. Accordingly, the entire amount of C is added in theform of a graphite powder.

As described above, according to the fifth embodiment of the presentinvention, the production method for the wear resistant sintered alloyincludes preparing an iron alloy powder, a hard phase forming alloypowder, and a graphite powder. The iron alloy powder consists of, bymass %, 1 to 7% of Mo and the balance of Fe and inevitable impurities.The hard phase forming alloy powder consists of, by mass %, 15 to 35% ofMo, 1 to 10% of Si, 10 to 40% of Cr, and the balance of Co andinevitable impurities. The production method further includes mixing 15to 45% of the hard phase forming alloy powder and 0.5 to 1.5% of thegraphite powder with the iron alloy powder into a raw powder. Theproduction method further includes compacting the raw powder into agreen compact having a predetermined shape and includes sintering thegreen compact.

As described above, according to the fifth embodiment of the presentinvention, the wear resistant sintered alloy consists of, by mass %, 1.5to 18% of Cr, 3.09 to 19.57% of Mo, 0.15 to 4.5% of Si, 2.25 to 33.3% ofCo, 0.5 to 1.5% of C, and the balance of Fe and inevitable impurities.The wear resistant sintered alloy exhibits a metallic structure in which15 to 45% of a hard phase is dispersed in an Fe—Mo—C alloy matrix, andthe hard phase consists of 15 to 35% of Mo, 1 to 10% of Si, 10 to 40% ofCr, and the balance of Co and inevitable impurities.

When Ni is solid-solved in an Fe matrix, Ni strengthens the Fe matrixand improves the quenchability of the matrix. In the wear resistantsintered alloy according to the fifth embodiment of the presentinvention, in a case of improving wear resistance and mechanicalstrength by forming a matrix structure made of a martensite structure ora mixed structure of a martensite structure and a bainite structure,instead of forming a matrix structure made of a bainite structure, Ni isadded. Ni having such effects is dispersed into Fe at relatively highrate in sintering. In addition, if Ni is added and is solid-solved inthe above iron alloy powder, the iron alloy powder is hardened, and thecompressibility of the main raw powder is decreased. Therefore, Ni isadded by adding a nickel powder to the iron alloy powder. In this case,when the nickel powder is added to the raw powder at more than 5%, alarge amount of Ni-rich austenite having low wear resistance is formedand remains in the matrix. Therefore, the upper limit of the amount ofthe nickel powder added to the raw powder is set to be 5%.

Examples Example A Hard Phase Forming Alloy Powder Example A-1

An iron powder, a copper powder, a graphite powder, and a hard phaseforming alloy powder having a composition shown in Table A-1 wereprepared. The iron powder, 1.5% of the copper powder, 35% of the hardphase forming alloy powder, and 1% of the graphite powder were added andmixed with a forming lubricant (0.8% of zinc stearate), and a raw powderwas obtained. The obtained raw powder was compacted at a compactingpressure of 650 MPa so as to be formed in a ring shape with an outerdiameter of 30 mm, an inner diameter of 20 mm, and a height of 10 mm.Next, these green compacts were sintered at 1160° C. for 60 minutes in adecomposed ammonia gas atmosphere, and samples Nos. A01 to A07 wereformed. Simple wear tests and corrosion tests were performed on thesesamples. The results of these tests are shown in Table A-1.

The simple wear tests were performed with the input of colliding andsliding under high temperature. Specifically, the above-describedring-shaped samples (sintered alloys) were formed in a valve sheet inwhich the inner edge part has a tapered surface of 45°. The valve sheetswere pressed into and were fitted into a housing made of an aluminumalloy. Then, discoid mating materials (valves) in which the outer edgepartially has a tapered surface of 45° were made from SUH-36. The matingmaterial was moved up and down by rotation of an eccentric cam driven bya motor so that the tapered surface of the sintered alloy and the matingmaterial collided repeatedly. That is, the movement of the valve is apiston movement up and down, and the valve repeats an action of leavingfrom the valve sheet by rotation of the eccentric cam driven by themotor and an action of colliding with the valve sheet by a valve spring.In these tests, the mating materials were heated with a burner so thatthe sintered alloys reached 350° C. The colliding frequency was 2800times per minute, and the repeating time was 10 hours. After these testswere performed, the wear amounts of the valve sheets and wear amounts ofthe valves were measured and evaluated. In corrosion tests, ring-shapedsamples were immersed in a 10% nitric acid solution for one hour, andweight changes were measured before and after the immersing. The weightchanges were divided by the surface area, and these calculated valueswere evaluated as a corrosion loss (mg/cm²).

TABLE A-1 Compositions of hard phase Wear amount forming alloy powderSubstitutional μm Corrosion Sample mass % ratio Valve loss No. Co Fe CrMo Si of Fe sheet Valve Total mg/cm² Notes A01 Balance — 8.0 28.0 2.5 —45 3 48 0.35 Conventional example A02 Balance 26.0 5.0 20.0 3.0 36 115 3118 0.51 Comparative example A03 Balance 24.0 10.0 20.0 3.0 36 80 3 830.38 Comparative example A04 Balance 20.6 20.0 20.0 3.0 36 42 3 45 0.15Practical example A05 Balance 17.0 30.0 20.0 3.0 36 35 3 38 0.13Practical example A06 Balance 13.4 40.0 20.0 3.0 36 45 5 50 0.16Practical example A07 Balance 9.7 50.0 20.0 3.0 36 99 21 120 0.21Comparative example

In the sample No. A01 in Table A-1, a conventional hard phase formingalloy powder was used. In the samples Nos. A02 to A07, the amount of Moin a conventional hard phase forming alloy powder was decreased, 36% ofCo was substituted by Fe, and the amount of Cr was changed in the rangeof 5 to 50%. According to these samples, the influence of the amount ofCr in the hard phase forming alloy powder was investigated.

In the sample No. A02 in which the amount of Cr in the hard phaseforming alloy powder was 5%, the wear amount of the valve sheet waslarge because Fe was included in the hard phase forming alloy powder andthe amount of Cr was insufficient. Moreover, the corrosion loss waslarge because Fe was included in the hard phase forming alloy powder. Inthe sample No. A03 in which the amount of Cr in the hard phase formingalloy powder was 10%, the amount of Cr was increased, whereby the wearamount of the valve sheet and the corrosion loss were decreased, butthese values were large. On the other hand, in the samples Nos. A04 toA06 in which the amount of Cr in the hard phase forming alloy powder was20 to 40%, the wear amount was equal to or less than that of the sampleNo. A01 (conventional example) because the matrix was strengthened byCr. Moreover, the corrosion loss was not more than half that of thesample No. A01 (conventional example) because corrosion resistance wasimproved by Cr. In the sample No. A06 in which the amount of Cr in thehard phase forming alloy powder was 40%, as described above, althoughwear resistance and corrosion resistance were good, the wear amount andthe corrosion loss were slightly increased, compared with the sample No.A05 in which the amount of Cr in the hard phase forming alloy powder was30%. This is because, in the sample No. A06, the oxide films on thesurfaces of the hard phase forming alloy powder particles were hardenedby the increase in the amount of Cr, whereby hardness of the hard phaseforming alloy powder was increased, and compressibility of the rawpowder was decreased. As a result, the density of the green compact wasdecreased, and the density of the sintered compact was decreased. In thesample No. A07 in which the amount of Cr in the hard phase forming alloypowder was greater than 40%, the influence of the decrease in thedensity of the sintered compact was remarkable, and the strength of thesintered compact was decreased. That is, the wear amount of the valvesheet was remarkably increased, and the wear amount of the valve wasalso remarkably increased because wear particles of the valve sheeteroded the valve. Moreover, pitting corrosion was easily caused, wherebythe corrosion loss was increased. According to the above results, whenthe amount of Cr in the hard phase forming alloy powder was 20 to 40%,the obtained sintered alloys had not less than approximately equal wearresistance and superior corrosion resistance, compared with a case ofusing the conventional hard phase forming alloy powder.

Example A-2

The iron powder, the copper powder, the graphite powder used in theexample A-1, and a hard phase forming alloy powder having a compositionshown in Table A-2 were added and mixed in the same ratio as in theexample A-1, and a raw powder was obtained. The obtained raw powder wascompacted and sintered in the same way as in the example A-1, andsamples Nos. A08 to A13 were formed. The wear tests were performed inthe same way as in the example A-1 for these samples. The results andthe values of the samples Nos. A01 and A05 are shown in Table A-2.

TABLE A-2 Compositions of hard phase forming Wear amount alloy powderSubstitutional μm Sample mass % ratio Valve No. Co Fe Cr Mo Si of Fesheet Valve Total Notes A01 Balance — 8.00 28.00 2.50 — 45 3 48Conventional example A08 Balance — 30.00 20.00 3.00 — 25 3 28 Practicalexample A09 Balance  7.00 30.00 20.00 3.00 15 30 3 33 Practical exampleA05 Balance 17.00 30.00 20.00 3.00 36 35 3 38 Practical example A10Balance 28.20 30.00 20.00 3.00 60 37 3 40 Practical example A11 Balance37.60 30.00 20.00 3.00 80 45 4 49 Comparative example A12 Balance 42.3030.00 20.00 3.00 90 78 5 83 Comparative example A13 — 47.00 30.00 20.003.00 100 171 10 181 Practical example

According to Table A-2, when Co in the hard phase forming alloy powderwas substituted by Fe, the influence of the substitutional ratio of Fewas investigated. The substitutional ratio is a percentage of the amountof Fe in the hard phase forming alloy powder to the sum total of theamount of Co and Fe in the hard phase forming alloy powder. In thesample No. A08, Co in the hard phase forming alloy powder was notsubstituted by Fe, and the wear amount was the least among the aboveexamples A and wear resistance was good. When Co in the hard phaseforming alloy powder was substituted by Fe and the substitutional ratioof Fe was increased, the wear amount was increased. In this case, whenthe substitutional ratio of Fe was not more than 80%, the wear amountwas approximately equal to or less than that of the sample No. A01(conventional example). However, when the substitutional ratio of Fe wasmore than 80%, the effect of Co was insufficient and the wear amount wasincreased remarkably. According to the above results, although Co in thehard phase forming alloy powder could be substituted by Fe, thesubstitutional ratio of Fe should be not more than 80%.

Example A-3

The iron powder, the copper powder, the graphite powder used in theexample A-1, and a hard phase forming alloy powder having a compositionshown in Table A-3 were added and mixed in the same ratio as in theexample A-1, and a raw powder was obtained. The obtained raw powder wascompacted and sintered in the same way as in the example A-1, andsamples Nos. A14 to A17 were formed. The wear tests were performed inthe same way as in the example A-1 for these samples. The results andthe values of the samples Nos. A01 and A05 are shown in Table A-3.

TABLE A-3 Compositions of hard phase forming Wear amount alloy powderSubstitutional μm Sample mass % ratio Valve No. Co Fe Cr Mo Si of Fesheet Valve Total Notes A01 Balance — 8.00 28.00 2.50 0.0 45 3 48Conventional example A05 Balance 17.00 30.00 20.00 3.00 36.2 35 3 38Practical example A14 Balance 17.00 30.00 20.00 3.00 36.2 32 3 35Practical example A15 Balance 17.00 30.00 20.00 3.00 36.2 27 4 31Practical example A16 Balance 17.00 30.00 20.00 3.00 36.2 35 12 47Practical example A17 Balance 17.00 30.00 20.00 3.00 36.2 68 46 114Comparative example

According to Table A-3, the effect of Mn in the hard phase forming alloypowder was investigated. In the samples Nos. A14 to A16 in which theamount of Mn in the hard phase forming alloy powder was not more than5%, the alloy matrixes of hard phases were strengthened by Mn, wherebythe wear amounts of the valve sheets were approximately equal to or lessthan that of the sample No. A05 in which Mn was not added in the hardphase forming alloy powder. On the other hand, the wear amounts of thevalves were slightly increased according to the increase in the amountof Mn because hard phases were strengthened. In the sample No. A17 inwhich the amount of Mn in the hard phase forming alloy powder wasgreater than 5%, the wear amount of the valve sheet was remarkablyincreased. This is because the hard phase forming alloy powder washardened by the increase in the amount of Mn, whereby compressibility ofthe raw powder was remarkably decreased. As a result, the density of thegreen compact was decreased, and the density of the sintered compact wasdecreased, whereby the strength of the sintered compact was decreased.Moreover, the wear amount of the valve was also remarkably increasedbecause the wear particles of the valve sheet eroded the valve.According to the above results, although wear resistance of the sinteredalloy could be further improved by adding Mn in the hard phase formingalloy powder, the amount of Mn in the hard phase forming alloy powdershould be not more than 5%.

Example B Fe—Ni—C Alloy Matrix Example B-1

An ore-reduced iron powder consisting of 1% of metal oxides and thebalance of Fe and inevitable impurities, a nickel powder, a hard phaseforming alloy powder having a composition shown in Table B-1, and agraphite powder were prepared. These powders were added and mixed with aforming lubricant (0.8% of zinc stearate) in the mixing ratio shown inTable B-1, and a raw powder was obtained. The obtained raw powder wascompacted and sintered in the same way as in the example A-1, andsamples Nos. B01 to B06 were formed. The simple wear tests and thecorrosion tests were performed in the same way as in the example A-1 forthese samples. In the simple wear tests, the mating materials wereheated with a burner so that the sintered alloys reached 300° C. Theresults of these tests are also shown in Table B-1.

TABLE B-1 Mixing ratio mass % Evaluation item Hard phase forming alloypowder Wear amount μm Corrosion Sample Iron Nickel Compositions mass %Graphite Valve loss No. powder powder Co Fe Cr Mo Si powder sheet ValveTotal mg/cm² Notes B01 Balance 2.00 35.00 Balance 42.00 5.00 20.00 3.001.00 98 3 101 0.32 Comparative example B02 Balance 2.00 35.00 Balance37.00 10.00 20.00 3.00 1.00 61 3 64 0.17 Practical example B03 Balance2.00 35.00 Balance 27.00 20.00 20.00 3.00 1.00 41 3 44 0.15 Practicalexample B04 Balance 2.00 35.00 Balance 17.00 30.00 20.00 3.00 1.00 30 333 0.13 Practical example B05 Balance 2.00 35.00 Balance 7.00 40.0020.00 3.00 1.00 47 5 52 0.16 Practical example B06 Balance 2.00 35.00Balance 2.00 45.00 20.00 3.00 1.00 85 21 106 0.20 Comparative example

According to Table B-1, the influence of the amount of Cr in the hardphase forming alloy powder (the amount of Cr in the hard phase) wasinvestigated. In the sample No. B01, the amount of Cr in the hard phaseforming alloy powder was insufficient, whereby the matrix of thesintered alloy was not sufficiently strengthened, and the wear amount ofthe valve sheet was large. In addition, since the amount of Cr wasinsufficient, the corrosion resistance was insufficient, and thecorrosion loss was also large. In the sample No. B02 in which the amountof Cr in the hard phase forming alloy powder was 10%, the wear amount ofthe valve sheet was remarkably decreased because the matrix wasstrengthened by Cr, and the corrosion loss was reduced because corrosionresistance was improved by Cr. When the amount of Cr in the hard phaseforming alloy powder was not more than 30%, the wear amounts of thevalve sheets and the corrosion losses were decreased according to theincrease in the amount of Cr. On the other hand, in the sample No. B05in which the amount of Cr in the hard phase forming alloy powder was40%, the wear amount of the valve sheet and the corrosion loss wereincreased. This is because the amount of Cr in the hard phase formingalloy powder was increased, whereby the hardness of the hard phaseforming alloy powder was increased. As a result, compressibility of theraw powder was decreased, and the density of the green compact wasdecreased, whereby the density of the sintered compact was decreased. Inthe sample No. B06 in which the amount of Cr in the hard phase formingalloy powder was greater than 40%, the wear amount of the valve sheetwas increased and the corrosion loss was remarkably increased, becausethe influence of the decrease of compressibility was remarkable.Moreover, the wear amount of the valve was also remarkably increasedbecause the wear particles of the valve sheet eroded the valve.According to the above results, when the amount of Cr in the hard phaseforming alloy powder was 10 to 40%, the wear amounts of the valve sheetand valve were small and the corrosion loss of the sintered alloy wassmall.

Example B-2

The ore-reduced iron powder used in the example B-1, a nickel powder, agraphite powder, and the hard phase forming alloy powder used in thesample No. B04 in the example B-1 were prepared. The ratio of the hardphase forming alloy powder was changed as shown in Table B-2, thesepowders were added and mixed with a forming lubricant (0.8% of zincstearate), and a raw powder was obtained. The obtained raw powder wascompacted and sintered in the same way as in the example A-1, andsamples Nos. B07 to B11 were formed. The wear tests and the corrosiontests were performed in the same way as in the example B-1 for thesesamples. The results are shown in Table B-2 with the values of thesample No. B04 in the example B-1.

TABLE B-2 Mixing ratio mass % Evaluation item Hard phase forming alloypowder Wear amount μm Corrosion Sample Iron Nickel Compositions mass %Graphite Valve loss No. powder powder Co Fe Cr Mo Si powder sheet ValveTotal mg/cm² Notes B07 Balance 2.00 5.00 Balance 17.00 30.00 20.00 3.001.00 120 0 120 0.56 Comparative example B08 Balance 2.00 15.00 Balance17.00 30.00 20.00 3.00 1.00 58 2 60 0.28 Practical example B09 Balance2.00 25.00 Balance 17.00 30.00 20.00 3.00 1.00 35 3 38 0.18 Practicalexample B04 Balance 2.00 35.00 Balance 17.00 30.00 20.00 3.00 1.00 30 333 0.13 Practical example B10 Balance 2.00 45.00 Balance 17.00 30.0020.00 3.00 1.00 49 6 55 0.15 Practical example B11 Balance 2.00 55.00Balance 17.00 30.00 20.00 3.00 1.00 90 35 125 0.26 Comparative example

According to Table B-2, the influence of the amount of the hard phaseforming alloy powder (the amount of the hard phase dispersed in thematrix) was investigated. In the sample No. B07 in which the amount ofthe hard phase forming alloy powder was less than 15%, the wear amountof the valve sheet was large because the amount of the hard phase wasinsufficient and the plastic flow of the matrix could not be prevented.Moreover, the corrosion loss was large because the hard phase wasinsufficient and Cr was not sufficiently dispersed from the hard phaseto the matrix. In the sample No. B08 in which the amount of the hardphase forming alloy powder was 15%, wear resistance and corrosionresistance of the matrix of the sintered alloy were improved by the hardphase, whereby the wear amount of the valve sheet was remarkablydecreased and the corrosion loss was decreased. When the amount of thehard phase forming alloy powder was not more than 35%, the wear amountof the valve sheet and the corrosion loss were decreased according tothe increase in the amount of the hard phase forming alloy powder. Onthe other hand, in the sample No. B10 in which the amount of the hardphase forming alloy powder was 45%, the wear amount of the valve sheetand the corrosion loss were slightly increased because compressibilityof the raw powder was decreased by the increase in the amount of thehard phase forming alloy powder. In the sample No. B11 in which theamount of the hard phase forming alloy powder was greater than 45%, theinfluence of the decrease of compressibility was remarkable, whereby thewear amount of the valve sheet was remarkably increased, and thecorrosion loss was increased. Moreover, the wear amount of the valvealso was remarkably increased because the wear particles of the valvesheet eroded the valve. According to the above results, when the amountof the hard phase forming alloy powder (the amount of the hard phasedispersed in the matrix) was 15 to 45%, the wear amounts of the valvesheet and the valve were small.

Example B-3

The ore-reduced iron powder used in the example B-1, a nickel powder, agraphite powder, and the hard phase forming alloy powder used in thesample No. B04 in the example B-1 were prepared. The ratio of the nickelpowder was changed as shown in Table B-3, these powders were added andmixed with a forming lubricant (0.8% of zinc stearate), and a raw powderwas obtained. The obtained raw powder was compacted and sintered in thesame way as in the example A-1, and samples Nos. B12 to B17 were formed.The wear tests were performed in the same way as in the example B-1 forthese samples. The results are shown in Table B-3 with the values of thesample No. B04 in the example B-1.

TABLE B-3 Mixing ratio mass % Evaluation item Hard phase forming alloypowder Wear amount μm Sample Iron Nickel Compositions mass % GraphiteValve No. powder powder Co Fe Cr Mo Si powder sheet Valve Total NotesB12 Balance — 35.00 Balance 17.00 30.00 20.00 3.00 1.00 102 2 104Comparative example B13 Balance 1.00 35.00 Balance 17.00 30.00 20.003.00 1.00 51 3 54 Practical example B04 Balance 2.00 35.00 Balance 17.0030.00 20.00 3.00 1.00 30 3 33 Practical example B14 Balance 3.00 35.00Balance 17.00 30.00 20.00 3.00 1.00 26 3 29 Practical example B15Balance 4.00 35.00 Balance 17.00 30.00 20.00 3.00 1.00 33 3 36 Practicalexample B16 Balance 5.00 35.00 Balance 17.00 30.00 20.00 3.00 1.00 56 460 Practical example B17 Balance 6.00 35.00 Balance 17.00 30.00 20.003.00 1.00 94 5 99 Comparative example

According to Table B-3, the influence of the amount of the nickel powder(the amount of Ni in the overall composition) was investigated. In thesample No. B12 in which the nickel powder was not added, the wear amountof the valve sheet was large because the Fe matrix of the sintered alloywas not strengthened. In the sample No. B13 in which the amount of thenickel powder was 1%, the wear amount of the valve sheet was remarkablydecreased because the Fe matrix was strengthened by Ni. When the amountof the nickel powder was not more than 3%, the wear amount of the valvesheet was decreased according to the increase in the amount of thenickel powder. On the other hand, in the samples Nos. B15 and B16 inwhich the amount of the nickel powder was 4 to 5%, the wear amounts ofthe valve sheet were slightly increased because the amount of softresidual austenite phase was increased. In the sample No. B17 in whichthe amount of the nickel powder was greater than 5%, the wear amount ofthe valve sheet was remarkably increased because the amount of the softresidual austenite phase was too large. According to the above results,when the amount of the nickel powder (the amount of Ni in the overallcomposition) was 1 to 5%, the wear amount of the valve sheet was small.

Example B-4

The ore-reduced iron powder used in the example B-1, a nickel powder, agraphite powder, and the hard phase forming alloy powder used in thesample No. B04 in the example B-1 were prepared. The ratio of thegraphite powder was changed as shown in Table B-4, these powders wereadded and mixed with a forming lubricant (0.8% of zinc stearate), and araw powder was obtained. The obtained raw powder was compacted andsintered in the same way as in the example A-1, and samples Nos. B18 toB23 were formed. The wear tests were performed in the same way as in theexample B-1 for these samples. The results are shown in Table B-4 withthe values of the sample No. B04 in the example B-1.

TABLE B-4 Mixing ratio mass % Evaluation item Hard phase forming alloypowder Wear amount μm Sample Iron Nickel Compositions mass % GraphiteValve No. powder powder Co Fe Cr Mo Si powder sheet Valve Total NotesB18 Balance 2.00 35.00 Balance 17.00 30.00 20.00 3.00 0.30 125 2 127Comparative example B19 Balance 2.00 35.00 Balance 17.00 30.00 20.003.00 0.50 67 3 70 Practical example B20 Balance 2.00 35.00 Balance 17.0030.00 20.00 3.00 0.80 36 3 39 Practical example B04 Balance 2.00 35.00Balance 17.00 30.00 20.00 3.00 1.00 30 3 33 Practical example B21Balance 2.00 35.00 Balance 17.00 30.00 20.00 3.00 1.20 36 4 40 Practicalexample B22 Balance 2.00 35.00 Balance 17.00 30.00 20.00 3.00 1.50 65 873 Practical example B23 Balance 2.00 35.00 Balance 17.00 30.00 20.003.00 1.80 113 42 155 Comparative example

According to Table B-4, the influence of the amount of the graphitepowder (the amount of C in the overall composition) was investigated. Inthe sample No. B18 in which the amount of the graphite powder was lessthan 0.5%, the wear amount of the valve sheet was large because Fematrix of the sintered alloy was not sufficiently strengthened. In thesample No. B19 in which the amount of the graphite powder was 0.5%, thewear amount of the valve sheet was remarkably decreased because the Fematrix of the sintered alloy was strengthened. When the amount of thegraphite powder was not more than 1.0%, the wear amount of the valvesheet was decreased according to the increase in the amount of thegraphite powder. On the other hand, in the samples Nos. B21 and B22 inwhich the amount of the graphite powder was greater than 1.0%, the wearamounts of valve sheet were increased because the Fe matrix of thesintered alloy was hardened and embrittled. In the sample No. B23 inwhich the amount of the graphite powder was greater than 1.5%, thistendency was more remarkable, and therefore the wear amount of the valvesheet was remarkably increased. Moreover, the wear amount of the valvewas also remarkably increased because the wear particles of the valvesheet eroded the valve. According to the above results, when the amountof the graphite powder (the amount of C in the overall composition) was0.5 to 1.5%, the wear amounts of the valve sheet and the valve weresmall.

Example B-5

The ore-reduced iron powder used in the example B-1, a nickel powder, agraphite powder, and a hard phase forming alloy powder having acomposition shown in Table B-5 were prepared. These powders were addedand mixed with a forming lubricant (0.8% of zinc stearate) in the mixingratio shown in Table B-5, and a raw powder was obtained. The obtainedraw powder was compacted and sintered in the same way as in the exampleA-1, and samples Nos. B24 to B29 were formed. The wear tests wereperformed in the same way as in the example B-1 for these samples. Theresults are shown in Table B-5 with the values of the sample No. B04 inthe example B-1.

TABLE B-5 Mixing ratio mass % Hard phase forming alloy powder Evaluationitem Compositions Substitutional Wear amount μm Sample Iron Nickel mass% ratio Graphite Valve No. powder powder Co Fe Cr Mo Si of Fe powdersheet Valve Total Notes B24 Balance 2.00 35.00 Balance 0.00 30.00 20.003.00 0.00 1.00 21 3 24 Comparative example B25 Balance 2.00 35.00Balance 7.00 30.00 20.00 3.00 14.90 1.00 26 3 29 Practical example B04Balance 2.00 35.00 Balance 17.00 30.00 20.00 3.00 36.20 1.00 30 3 33Practical example B26 Balance 2.00 35.00 Balance 27.00 30.00 20.00 3.0057.40 1.00 34 3 37 Practical example B27 Balance 2.00 35.00 Balance37.00 30.00 20.00 3.00 78.70 1.00 57 4 61 Practical example B28 Balance2.00 35.00 Balance 42.00 30.00 20.00 3.00 89.40 1.00 101 5 106 Practicalexample B29 Balance 2.00 35.00 Balance 47.00 30.00 20.00 3.00 100.001.00 145 10 155 Comparative example

According to Table B-5, when Co in the hard phase forming alloy powderwas substituted by Fe, the influence of the substitutional ratio of Fewas investigated. In the sample No. B24 in which Co in the hard phaseforming alloy powder was not substituted by Fe, the total of the wearamounts was the least among the above examples B, and wear resistancewas good. When Co in the hard phase forming alloy powder was substitutedby Fe and the substitutional ratio of Fe was increased, the total of thewear amounts was increased. In this case, when the substitutional ratioof Fe was not more than 80%, wear amounts were not a problem inpractical use. On the other hand, when the substitutional ratio of Fewas more than 80%, the wear amounts were remarkably increased becausethe effect of Co was insufficient. According to the above results,although Co in the hard phase forming alloy powder could be substitutedby Fe, the substitutional ratio of Fe should be not more than 80%.

Example B-6

The ore-reduced iron powder used in the example B-1, a nickel powder, agraphite powder, and a hard phase forming alloy powder having acomposition shown in Table B-6 were prepared. These powders were addedand mixed with a forming lubricant (0.8% of zinc stearate) in the mixingratio shown in Table B-6, and a raw powder was obtained. The obtainedraw powder was compacted and sintered in the same way as in the exampleA-1, and samples Nos. B30 to B33 were formed. The wear tests wereperformed in the same way as in the example B-1 for these samples. Theresults are shown in Table B-6 with the values of the sample No. B04 inthe example B-1.

TABLE B-6 Mixing ratio mass % Evaluation item Hard phase forming alloypowder Wear amount μm Sample Iron Nickel Compositions mass % GraphiteValve No. powder powder Co Fe Cr Mo Si Mn powder sheet Valve Total NotesB04 Balance 2.00 35.00 Balance 17.00 30.00 20.00 3.00 — 1.00 30 3 33Practical example B30 Balance 2.00 35.00 Balance 17.00 30.00 20.00 3.001.00 1.00 27 3 30 Practical example B31 Balance 2.00 35.00 Balance 17.0030.00 20.00 3.00 3.00 1.00 23 4 27 Practical example B32 Balance 2.0035.00 Balance 17.00 30.00 20.00 3.00 5.00 1.00 28 10 38 Practicalexample B33 Balance 2.00 35.00 Balance 17.00 30.00 20.00 3.00 6.00 1.0054 46 100 Comparative example

According to Table B-6, the effect of Mn in the hard phase forming alloypowder was investigated. In the samples Nos. B30 to B32 in which theamount of Mn in the hard phase forming alloy powder was not more than5%, the alloy matrix of the hard phase was strengthened by Mn, wherebythe wear amounts of the valve sheets were less than that of the sampleNo. B04 in which Mn in the hard phase forming alloy powder was notadded. On the other hand, the wear amounts of the valves were slightlyincreased according to the increase in the amount of Mn because the hardphases were strengthened. In the sample No. B33 in which Mn in the hardphase forming alloy powder was more than 5%, the hard phase formingalloy powder was hardened, and the compressibility of the raw powder wasgreatly decreased. As a result, the wear amount of the valve sheet wasremarkably increased, and the wear amount of the valve was alsoremarkably increased because the wear particles of the valve sheeteroded the valve. According to the above results, although wearresistance of the sintered alloy could be further improved by adding Mnin the hard phase forming alloy powder, the amount of Mn in the hardphase forming alloy powder should be not more than 5%.

Example B-7

The nickel powder used in the example B-1, a hard phase forming alloypowder, a graphite powder, and an ore-reduced iron powder in which theamount of metal oxides was different as shown in Table B-7 wereprepared. These powders were added and mixed with a forming lubricant(0.8% of zinc stearate) in the mixing ratio shown in Table B-7, and araw powder was obtained. The obtained raw powder was compacted andsintered in the same way as in the example A-1, and samples Nos. B34 toB38 were formed. The wear tests were performed in the same way as in theexample B-1 for these samples. Moreover, in the example B-7,machinability tests were performed. In the machinability tests, holeswere made in the samples with a constant load by using a bench drill,and the numbers of the machined holes were compared. In these tests, theload was 1.3 kg, the drill was a carbide drill with a diameter of 3 mm,and the thickness of sample was 5 mm. The numbers of the machined holesin these machinability tests are shown in Table B-7.

TABLE B-7 Mixing ratio mass % Evaluation item Sam- Iron powder Hardphase forming alloy powder Wear amount μm Number of ple Metal NickelCompositions mass % Graphite Valve machined No. oxide powder Co Fe Cr MoSi powder sheet Valve Total holes Notes B34 Balance 0.20 2.00 35.00Balance 17.00 30.00 20.00 3.00 1.00 32 3 35 5 Comparative example B35Balance 0.30 2.00 35.00 Balance 17.00 30.00 20.00 3.00 1.00 31 3 34 11Practical example B04 Balance 1.00 2.00 35.00 Balance 17.00 30.00 20.003.00 1.00 30 3 33 20 Practical example B36 Balance 0.50 2.00 35.00Balance 17.00 30.00 20.00 3.00 1.00 30 3 33 15 Practical example B37Balance 1.50 2.00 35.00 Balance 17.00 30.00 20.00 3.00 1.00 41 10 51 23Practical example B38 Balance 2.00 2.00 35.00 Balance 17.00 30.00 20.003.00 1.00 95 36 131 25 Comparative example

According to Table B-7, the influence of the amount of metal oxides inthe ore-reduced iron powder (the amount of metal oxides in the matrix ofthe sintered alloy) was investigated. In the samples Nos. B34 to B36 andB04 in which the amount of metal oxides in the ore-reduced iron powderwas 0.2 to 1.0%, the wear amounts were approximately equal. On the otherhand, in the sample No. B37 in which the amount of metal oxides in theore-reduced iron powder was 1.5%, the iron powder was hardened by theincrease in the metal oxides in the ore-reduced iron powder, whereby thecompressibility of the raw powder was decreased, and the wear amountswere increased. In the sample No. B38 in which the amount of metaloxides in the ore-reduced iron powder was greater than 1.5%, the wearamount was remarkably increased because compressibility of the rawpowder was remarkably decreased. In the sample No. B34 in which theamount of metal oxides in the ore-reduced iron powder was 0.2%, therewere 5 machined holes, and the machinability was not good. On the otherhand, in the sample No. B35 in which the amount of metal oxides in theore-reduced iron powder was 0.3%, the number of the machined holes was11, and the machinability was improved and was more than twice thenumber of the machined holes of the sample No. B34. When the amount ofmetal oxides was further increased, the numbers of the machined holeswere increased and the machinability was improved. However, in thesample No. B38 in which the amount of metal oxides in the ore-reducediron powder was greater than 1.5%, the effect of the machinabilityimprovement was insufficient. Accordingly, the amount of metal oxides inthe ore-reduced iron powder (the amount of metal oxides in the matrix ofthe sintered alloy) was preferably not less than 0.3% from the viewpointof machinability, and preferably not more than 1.5% from the viewpointof wear resistance and machinability.

Example C Fe—Cr—C Alloy Matrix Example C-1

An iron alloy powder consisting of 3% of Cr and the balance of Fe andinevitable impurities, a hard phase forming alloy powder having acomposition shown in Table C-1, and a graphite powder were prepared. Theiron alloy powder, 35% of the hard phase forming alloy powder, and 1% ofthe graphite powder were added and mixed. Furthermore, 0.8 mass parts ofzinc stearate as a forming lubricant was added and mixed with 100 massparts of the mixed powder, and a raw powder was obtained. The obtainedraw powder was compacted and sintered in the same way as in the exampleA-1, and samples Nos. C01 to C06 were formed. The simple wear tests andthe corrosion tests were performed in the same way as in the example A-1for these samples. In the simple wear tests, the mating materials wereheated with a burner so that the sintered alloys reached 300° C., andthe colliding frequency was 3000 times per minute, and the time duringwhich this was conducted was 15 hours. The results of these tests arealso shown in Table C-1.

TABLE C-1 Mixing ratio mass % Evaluation item Hard phase forming alloypowder Wear amount μm Corrosion Sample Iron alloy Composition mass %Graphite Valve loss No. powder Co Fe Cr Mo Si powder sheet Valve Totalmg/cm² Notes C01 Balance 35.00 Balance 42.00 5.00 20.00 3.00 1.00 83 386 0.31 Comparative example C02 Balance 35.00 Balance 37.00 10.00 20.003.00 1.00 52 4 56 0.15 Practical example C03 Balance 35.00 Balance 27.0020.00 20.00 3.00 1.00 35 4 39 0.12 Practical example C04 Balance 35.00Balance 17.00 30.00 20.00 3.00 1.00 26 4 30 0.10 Practical example C05Balance 35.00 Balance 7.00 40.00 20.00 3.00 1.00 40 6 46 0.13 Practicalexample C06 Balance 35.00 Balance 2.00 45.00 20.00 3.00 1.00 72 25 970.23 Comparative example

According to Table C-1, the influence of the amount of Cr in the hardphase forming alloy powder (the amount of Cr in the hard phase) wasinvestigated. In the sample No. C01, the amount of Cr in the hard phaseforming alloy powder was insufficient, whereby corrosion resistance wasinsufficient and the corrosion loss was large. Moreover, since theamount of Cr was insufficient, the matrix of the sintered alloy was notsufficiently strengthened, and the wear amount of the valve sheet wasalso large. On the other hand, in the sample No. C02 in which the amountof Cr in the hard phase forming alloy powder was 10%, the corrosion losswas reduced because corrosion resistance was improved by Cr, and thewear amount of the valve sheet was remarkably decreased because thematrix was strengthened by Cr. When the amount of Cr in the hard phaseforming alloy powder was not more than 30%, the wear amounts of thevalve sheets were at low levels, and the corrosion losses were reducedto low levels according to the increase in the amount of Cr. In thesample No. C05 in which the amount of Cr in the hard phase forming alloypowder was 40%, the hardness of the hard phase forming alloy powder wasincreased by the increase in the amount of Cr in the hard phase formingalloy powder, whereby the compressibility of the raw powder wasdecreased, and the density of the green compact was decreased. As aresult, the density of the sintered compact was decreased, whereby thewear amount of the valve sheet and the corrosion loss were increased,but these values were sufficiently small. Moreover, the wear particlesof the valve sheet eroded the valve, and the wear amount of the valvewas also increased, but this value was small. In the sample No. C06 inwhich the amount of Cr in the hard phase forming alloy powder wasgreater than 40%, this tendency was more remarkable, and therefore thetotal of the wear amounts and the corrosion loss were remarkablyincreased. According to the above results, when the amount of Cr in thehard phase forming alloy powder was 10 to 40%, the wear amounts of thevalve sheet and the valve were small and the corrosion loss of thesintered alloy was small.

Example C-2

The iron alloy powder (Fe-3% Cr powder) used in the example C-1, thehard phase forming alloy powder (Co-30% Cr-20% Mo-17% Fe-3% Si powder)used in the sample No. C04 in the example C-1, and a graphite powderwere prepared. The ratio of the hard phase forming alloy powder waschanged as shown in Table C-2, and these powders were added and mixed.Furthermore, 0.8 mass parts of zinc stearate as a forming lubricant wasadded and mixed with 100 mass parts of the mixed powder, and a rawpowder was obtained. The obtained raw powder was compacted and sinteredin the same way as in the example A-1, and samples Nos. C07 to C11 wereformed. The wear tests and the corrosion tests were performed in thesame way as in the example C-1 for these samples. The results are shownin Table C-2 with the values of the sample No. C04 in the example C-1.

TABLE C-2 Mixing ratio mass % Hard phase Evaluation item forming Wearamount μm Corrosion Sample Iron alloy alloy Graphite Valve loss No.powder powder powder sheet Valve Total mg/cm² Notes C07 Balance 5.001.00 102 2 104 0.53 Comparative example C08 Balance 15.00 1.00 49 3 520.24 Practical example C09 Balance 25.00 1.00 30 4 34 0.14 Pracitcalexample C04 Balance 35.00 1.00 26 4 30 0.10 Practical example C10Balance 45.00 1.00 42 9 51 0.15 Practical example C11 Balance 55.00 1.0077 36 113 0.30 Comparative example

According to Table C-2, the influence of the amount of the hard phaseforming alloy powder (the amount of the hard phase dispersed in thematrix) was investigated. In the sample No. C07 in which the amount ofthe hard phase forming alloy powder was less than 15%, the wear amountof the valve sheet was large, because the amount of the hard phase wasinsufficient and the plastic flow of the matrix could not be prevented.Moreover, the corrosion loss was large, because the hard phase wasinsufficient and Cr was not sufficiently dispersed from the hard phaseto the matrix. On the other hand, in the sample No. C08 in which theamount of the hard phase forming alloy powder was 15%, wear resistanceand corrosion resistance of the matrix of the sintered alloy wereimproved by the hard phase, and the wear amount of the valve sheet wasremarkably decreased and the corrosion loss was decreased. When theamount of the hard phase forming alloy powder was not more than 35%, thewear amount of the valve sheet and the corrosion loss were decreasedaccording to the increase in the amount of the hard phase forming alloypowder. In the sample No. C10 in which the amount of the hard phaseforming alloy powder was 45%, compressibility of the raw powder wasdecreased by the increase in the amount of the hard phase forming alloypowder, whereby the wear amount of the valve sheet and the corrosionloss were slightly increased, but these were at low levels. In thesample No. C11 in which the amount of the hard phase forming alloypowder was greater than 45%, the wear amount of the valve sheet wasremarkably increased and the corrosion loss was increased, because theinfluence of the decrease of compressibility was remarkable. Moreover,the wear amount of the valve was also remarkably increased because thewear particles of the valve sheet eroded the valve. According to theabove results, when the amount of the hard phase forming alloy powder(the amount of the hard phase dispersed in the matrix) was 15 to 45%,the wear amounts of the valve sheet and the valve were small.

Example C-3

An iron alloy powder having a composition shown in Table C-3, a graphitepowder, and the hard phase forming alloy powder (Co-30% Cr-20% Mo-17%Fe-3% Si powder) used in the sample No. C04 in the example C-1 wereprepared. The iron alloy powder, 35% of the hard phase forming alloypowder, and 1% of the graphite powder were added and mixed. Furthermore,0.8 mass parts of zinc stearate as a forming lubricant was added andmixed with 100 mass parts of the mixed powder, and a raw powder wasobtained. The obtained raw powder was compacted and sintered in the sameway as in the example A-1, and samples Nos. C12 to C17 were formed. Thewear tests and the corrosion tests were performed in the same way as inthe example C-1 for these samples. The results are shown in Table C-3with the values of the sample No. C04 in the example C-1.

TABLE C-3 Mixing ratio mass % Hard phase Evaluation item Iron alloypowder forming Wear amount μm Corrosion Sample compositions alloyGraphite Valve loss No. Fe Cr powder powder sheet Valve Total mg/cm²Notes C12 Balance Balance 0.00 35.00 1.00 103 3 106 0.22 Comparativeexample C13 Balance Balance 1.00 35.00 1.00 43 4 47 0.16 Practicalexample C14 Balance Balance 2.00 35.00 1.00 30 4 34 0.13 Practicalexample C04 Balance Balance 3.00 35.00 1.00 26 4 30 0.10 Practicalexample C15 Balance Balance 4.00 35.00 1.00 29 4 33 0.09 Practicalexample C16 Balance Balance 5.00 35.00 1.00 48 5 53 0.16 Practicalexample C17 Balance Balance 6.00 35.00 1.00 80 6 86 0.25 Comparativeexample

According to Table C-3, the influence of the amount of Cr in the ironalloy powder was investigated. In the sample No. C12 using a pure ironpowder in which Cr was not added, the wear amount of the valve sheet andthe corrosion loss were large because Fe matrix of the sintered alloywas not strengthened. In the sample No. C13 in which the amount of Cr inthe iron alloy powder was 1%, the wear amount of the valve sheet wasremarkably decreased because the Fe matrix was strengthened by Cr, andthe corrosion loss was decreased because the corrosion resistance of theFe matrix was improved. When the amount of Cr in the iron alloy powderwas not more than 3%, the wear amount of the valve sheet and thecorrosion loss were decreased according to the increase in the amount ofCr in the iron alloy powder. In the samples Nos. C15 and C16 in whichthe amount of Cr in the iron alloy powder was 4 to 5%, the hardness ofthe iron alloy powder was increased, whereby compressibility of the rawpowder was decreased, and the density of the green compact wasdecreased. As a result, the density of the sintered compact wasdecreased, whereby the wear amount of the valve sheet and the corrosionloss were slightly increased, but these were at low levels. On the otherhand, in the sample No. C17 in which the amount of Cr in the iron alloypowder was greater than 5%, the influence of the. increase in thehardness of the iron alloy powder was remarkable, and the density of thesintered compact was remarkably decreased, whereby the wear amount ofthe valve sheet and the corrosion loss were remarkably increased.According to the above results, when the amount of Cr in the iron alloypowder was 1 to 5%, the wear amount of the valve sheet was small and thecorrosion loss was reduced.

Example C-4

The iron alloy powder (Fe-3% Cr powder) used in the example C-1, thehard phase forming alloy powder (Co-30% Cr-20% Mo-17% Fe-3% Si powder)used in the sample No. C04 in the example C-1, and a graphite powderwere prepared. The ratio of the graphite powder was changed as shown inTable C-4, and these powders were added and mixed. Furthermore, 0.8 massparts of zinc stearate as a forming lubricant was added and mixed with100 mass parts of the mixed powder, and a raw powder was obtained. Theobtained raw powder was compacted and sintered in the same way as in theexample A-1, and samples Nos. C18 to C23 were formed. The wear testswere performed in the same way as in the example C-1 for these samples.The results are shown in Table C-4 with the values of the sample No. C04in the example C-1.

TABLE C-4 Mixing ratio mass % Hard phase Evaluation item forming Wearamount μm Iron alloy alloy Graphite Valve Sample No. powder powderpowder sheet Valve Total Notes C18 Balance 35.00 0.30 107 3 110Comparative example C19 Balance 35.00 0.50 57 4 61 Practical example C20Balance 35.00 0.80 31 4 35 Practical example C04 Balance 35.00 1.00 26 430 Practical example C21 Balance 35.00 1.20 30 5 35 Practical exampleC22 Balance 35.00 1.50 55 9 64 Practical example C23 Balance 35.00 1.8096 43 139 Comparative example

According to Table C-4, the influence of the amount of the graphitepowder (the amount of C in the overall composition) was investigated. Inthe sample No. C18 in which the amount of the graphite powder was lessthan 0.5%, the wear amount of the valve sheet was large because Fematrix of the sintered alloy was not sufficiently strengthened. However,in the sample No. C19 in which the amount of the graphite powder was0.5%, the wear amount of the valve sheet was remarkably decreasedbecause Fe matrix of the sintered alloy was strengthened. When theamount of the graphite powder was not more than 1.0%, the wear amount ofthe valve sheet was decreased according to the increase in the amount ofthe graphite powder. In the sample in which the amount of the graphitepowder was 1.2 to 1.5%, the wear amount of the valve sheet was increasedand the wear amount of the valve was slightly increased because Fematrix of the sintered alloy was hardened and embrittled. In this case,the total of the wear amounts was not a problem in practical use. On theother hand, in the sample No. C23 in which the amount of the graphitepowder was greater than 1.5%, this tendency was more remarkable, andtherefore the wear amount of the valve sheet was remarkably increased.Moreover, the wear amount of the valve was also remarkably increasedbecause the wear particles of the valve sheet eroded the valve.According to the above results, when the amount of the graphite powder(the amount of C in the overall composition) was 0.5 to 1.5%, the wearamounts of the valve sheet and the valve were small.

Example C-5

The iron alloy powder (Fe-3% Cr powder) used in the example C-1, agraphite powder, and a hard phase forming alloy powder as shown in TableC-5 were prepared. The hard phase forming alloy powder has a compositionin which a ratio of Co and Fe was different from that of the hard phaseforming alloy powder (Co-30% Cr-20% Mo-17% Fe-3% Si powder) used in thesample No. C04 in the example C-1. The iron alloy powder, 35% of thehard phase forming alloy powder, and 1% of the graphite powder wereadded and were mixed. Furthermore, 0.8 mass parts of zinc stearate as aforming lubricant was added and mixed with 100 mass parts of the mixedpowder, and a raw powder was obtained. The obtained raw powder wascompacted and sintered in the same way as in the example A-1, andsamples Nos. C24 to C29 were formed. The wear tests were performed inthe same way as in the example C-1 for these samples. The results areshown in Table C-5 with the values of the sample No. C04 in the exampleC-1.

TABLE C-5 Mixing ratio mass % Evaluation item Hard phase forming alloypowder Wear amount μm Sample Iron alloy Compositions mass %Substitutional Graphite Valve No. powder Co Fe Cr Mo Si ratio of Fepowder sheet Valve Total Notes C24 Balance 35.00 Balance 0.00 30.0020.00 3.00 0.00 1.00 18 3 21 Comparative example C25 Balance 35.00Balance 7.00 30.00 20.00 3.00 14.90 1.00 22 4 26 Practical example C04Balance 35.00 Balance 17.00 30.00 20.00 3.00 36.20 1.00 26 4 30Practical example C26 Balance 35.00 Balance 28.00 30.00 20.00 3.00 59.601.00 29 4 33 Practical example C27 Balance 35.00 Balance 37.50 30.0020.00 3.00 79.80 1.00 46 5 51 Practical example C28 Balance 35.00Balance 42.00 30.00 20.00 3.00 89.40 1.00 86 6 92 Practical example C29Balance 35.00 Balance 47.00 30.00 20.00 3.00 100.00 1.00 123 11 134Comparative example

According to Table C-5, when Co in the hard phase forming alloy powderwas substituted by Fe, the influence of the substitutional ratio of Fewas investigated. In the sample No. C24 in which Co in the hard phaseforming alloy powder was not substituted by Fe, the wear amounts werethe least among the above examples C, and wear resistance was good. WhenCo in the hard phase forming alloy powder was substituted by Fe and thesubstitutional ratio of Fe was increased, the wear amounts wereincreased. In this case, when the substitutional ratio of Fe was notmore than 80% (samples Nos. C04 and C25 to C27), the wear amounts werenot problem in practical use. However, in the samples Nos. C28 and C29in which the substitutional ratio of Fe was more than 80%, the wearamounts were remarkably increased because the effect of Co wasinsufficient. According to the above results, although Co in the hardphase forming alloy powder could be substituted by Fe, thesubstitutional ratio of Fe should be not more than 80%. Furthermore, thesubstitutional ratio of Fe was preferably not more than 60%.

Example C-6

The iron alloy powder (Fe-3% Cr powder) used in the example C-1, agraphite powder, and a hard phase forming alloy powder as shown in TableC-6 were prepared. The hard phase forming alloy powder was formed byadding different amount of Mn in the hard phase forming alloy powder(Co-30% Cr-20% Mo-17% Fe-3% Si powder) used in the sample No. C04 in theexample C-1. The iron alloy powder, 35% of the hard phase forming alloypowder, and 1% of the graphite powder were added and mixed. Furthermore,0.8 mass parts of zinc stearate as a forming lubricant was added andmixed with 100 mass parts of the mixed powder, and a raw powder wasobtained. The obtained raw powder was compacted and sintered in the sameway as in the example A-1, and samples Nos. C30 to C33 were formed. Thewear tests were performed in the same way as in the example C-1 forthese samples. The results are shown in Table C-6 with the values of thesample No. C04 in the example C-1.

TABLE C-6 Mixing ratio mass % Evaluation item Hard phase forming alloypowder Wear amount μm Sample Iron alloy Compositions mass % GraphiteValve No. powder Co Fe Cr Mo Si Mn powder sheet Valve Total Notes C04Balance 35.00 Balance 17.00 30.00 20.00 3.00 — 1.00 26 4 30 Practicalexample C30 Balance 35.00 Balance 17.00 30.00 20.00 3.00 1.00 1.00 23 528 Practical example C31 Balance 35.00 Balance 17.00 30.00 20.00 3.003.00 1.00 20 5 25 Practical example C32 Balance 35.00 Balance 17.0030.00 20.00 3.00 5.00 1.00 24 11 35 Practical example C33 Balance 35.00Balance 17.00 30.00 20.00 3.00 7.00 1.00 46 49 95 Comparative example

According to Table C-6, the effect of Mn added in the hard phase formingalloy powder (the hard phase) was investigated. In the samples Nos. C30to C32 in which the amount of Mn in the hard phase forming alloy powderwas not more than 5%, the alloy matrix of the hard phase wasstrengthened by Mn, whereby the wear amounts of the valve sheets wereless than that of the sample No. C04 in which Mn in the hard phaseforming alloy powder was not added. On the other hand, the wear amountsof the valves were slightly increased according to the increase in theamount of Mn, because the hard phase was strengthened. In the sample No.C33 in which the amount of Mn in the hard phase forming alloy powder wasgreater than 5%, the hard phase forming alloy powder was hardened,whereby compressibility of the raw powder was decreased. Therefore, thewear amount of the valve sheet was remarkably increased, and the wearamount of the valve was also remarkably increased because the wearparticles of the valve sheet eroded the valve. According to the aboveresults, although wear resistance of the sintered alloy could be furtherimproved by adding Mn in the hard phase forming alloy powder, the amountof Mn in the hard phase forming alloy powder should be not more than 5%.

Example C-7

An iron alloy powder having a composition shown in Table C-7, the hardphase forming alloy powder (Co-30% Cr-20% Mo-17% Fe-3% Si powder) usedin the sample No. C04 in the example C-1, and a graphite powder wereprepared. The iron alloy powder was formed by adding at least one of Mo,V, and Nb in the iron alloy powder (Fe-3% Cr powder) used in the exampleC-1. The iron alloy powder, 35% of the hard phase forming alloy powder,and 1% of the graphite powder were added and mixed. Furthermore, 0.8mass parts of zinc stearate as a forming lubricant was added and mixedwith 100 mass parts of the mixed powder, and a raw powder was obtained.The obtained raw powder was compacted and sintered in the same way as inthe example A-1, and samples Nos. C34 to C44 were formed. The wear testswere performed in the same way as in the example C-1 for these samples.The results are shown in Table C-7 with the values of the sample No. C04in the example C-1.

TABLE C-7 Mixing ratio mass % Hard phase Evaluation item Iron alloypowder forming Wear amount μm Sample Compositions mass % alloy GraphiteValve No. Fe Cr Mo V Nb powder powder sheet Valve Total Notes C04Balance Balance 3.00 — — — 35.00 1.00 26 4 30 Practical example C34Balance Balance 3.00 0.50 — — 35.00 1.00 22 5 27 Practical example C35Balance Balance 3.00 0.50 0.50 — 35.00 1.00 18 7 25 Practical exampleC36 Balance Balance 3.00 0.50 — 0.50 35.00 1.00 19 6 25 Practicalexample C37 Balance Balance 3.00 0.50 0.50 0.50 35.00 1.00 15 11 26Practical example C38 Balance Balance 3.00 1.00 — — 35.00 1.00 18 7 25Practical example C39 Balance Balance 3.00 1.50 — — 35.00 1.00 14 10 24Practical example C40 Balance Balance 3.00 2.00 — — 35.00 1.00 13 15 28Practical example C41 Balance Balance 3.00 1.50 0.50 — 35.00 1.00 13 1326 Practical example C42 Balance Balance 3.00 2.00 1.00 — 35.00 1.00 1821 39 Comparative example C43 Balance Balance 3.00 2.40 — — 35.00 1.0013 15 28 Practical example C44 Balance Balance 3.00 3.00 — — 35.00 1.0016 25 41 Comparative example

According to samples Nos. C04, C34, C38 to C40, C43, and C44 in TableC-7, the effect of the amount of Mo in the iron alloy powder wasinvestigated. In these samples, compared with the sample No. C04 inwhich Mo was not added in the iron alloy powder, when Mo was added inthe iron alloy powder and the amount of Mo was increased, the wearamounts of the valves were slightly increased, but the wear amounts ofvalve sheets were decreased and the totals of the wear amounts weredecreased. However, in the sample No. C44 in which the amount of Mo inthe iron alloy powder was greater than 2.4%, the wear amount of thevalve sheet was increased and the total of the wear amounts wasincreased.

The sample No. C38 included Mo in the iron alloy powder at 1%, and thesample No. C35 included Mo in the iron alloy powder at 0.5% and includedV in the iron alloy powder at 0.5% (the total amount of Mo and V was1.0%). The sample No. C36 included Mo in the iron alloy powder at 0.5%and included Nb in the iron alloy powder at 0.5% (the total amount of Moand Nb was 1.0%). In these samples Nos. C38, C35, and C36, the wearamounts of the valve sheets were approximately equal and the wearamounts of the valves were approximately equal. The sample No. C39included Mo in the iron alloy powder at 1.5%, and the sample No. C37included Mo, V, and Nb in the iron alloy powder at respectively 0.5%(the total amount of Mo, V, and Nb was 1.5%). In these samples Nos. C39and C37, the wear amounts of the valve sheets were approximately equaland the wear amounts of the valves were approximately equal. The sampleNo. C42 included Mo in the iron alloy powder at 2.0%, and the sample No.C41 included Mo in the iron alloy powder at 1.5% and included V in theiron alloy powder at 0.5% (the total amount of Mo and V was 2.0%). Inthese samples Nos. C42 and C41, the wear amounts of the valve sheetswere approximately equal and the wear amounts of the valves wereapproximately equal. The sample No. C44 included Mo in the iron alloypowder at 3.0%, and the sample No. C42 included Mo in the iron alloypowder at 2.0% and included V in the iron alloy powder at 1.0% (thetotal amount of Mo and V was 3.0%). In these samples Nos. C44 and C42,the wear amounts of valve sheets were approximately equal, the wearamounts of valves were approximately equal, and the totals of the wearamounts were increased. Accordingly, Mo, V, and Nb in the iron alloypowder had approximately equal effects, and the wear resistance wasimproved when the total amount of Mo, V, and Nb in the iron alloy powderwas not more than 2.4%.

Example C-8

The iron alloy powder (Fe-3% Cr powder) used in the example C-1, thehard phase forming alloy powder (Co-30% Cr-20% Mo-17% Fe-3% Si powder)used in the sample No. C04 in the example C-1, a graphite powder, and anickel powder were prepared. The iron alloy powder, 35% of the hardphase forming alloy powder, 1% of the graphite powder, and a ratio shownin Table C-8 of the nickel powder were added and mixed. Furthermore, 0.8mass parts of zinc stearate as a forming lubricant was added and mixedwith 100 mass parts of the mixed powder, and a raw powder was obtained.The obtained raw powder was compacted and sintered in the same way as inthe example A-1, and samples Nos. C45 to C50 were formed. The wear testswere performed in the same way as in the example C-1 for these samples.The results are shown in Table C-8 with the values of the sample No. C04in the example C-1.

TABLE C-8 Mixing ratio mass % Hard phase Evaluation item forming Wearamount μm Sample Iron alloy alloy Graphite Nickel Valve No. powderpowder powder powder sheet Valve Total Notes C04 Balance 35.00 1.00 0.0026 4 30 Practical example C45 Balance 35.00 1.00 1.00 23 4 27 Practicalexample C46 Balance 35.00 1.00 2.00 22 4 26 Practical example C47Balance 35.00 1.00 3.00 21 4 25 Practical example C48 Balance 35.00 1.004.00 22 4 26 Practical example C49 Balance 35.00 1.00 5.00 25 5 30Practical example C50 Balance 35.00 1.00 7.00 67 8 75 Comparativeexample

According to Table C-8, compared with the sample No. C04 in which thenickel powder was not added to the raw powder and Ni was not added inthe matrix, in the samples Nos. C45 to C49, in which the nickel powderwas added at not more than 5%, the wear amounts of the valve sheets weredecreased and the totals of the wear amounts were decreased. In thesample No. C50 in which the amount of the nickel powder was greater than5%, a large amount of Ni-rich austenite having low wear resistance wasformed and remained in the matrix, whereby the wear resistance of thevalve sheet was decreased and the wear amount of the valve sheet wasincreased. Moreover, the amount of hard martensite was increased, andthe degree of erosion of the valve (the mating material) was increased,whereby the wear amount of the valve was increased and the total of thewear amounts was remarkably increased. Accordingly, although wearresistance was improved by adding the nickel powder, the amount of thenickel powder should be not more than 5.0%.

Example D Fe—Co—C Alloy Matrix Example D-1

An iron alloy powder consisting of 6.5% of Co, 1.5% of Ni, 1.5% of Mo,and the balance of Fe and inevitable impurities, a hard phase formingalloy powder having a composition shown in Table D-1, and a graphitepowder were prepared. The iron alloy powder, 35% of the hard phaseforming alloy powder, and 1% of the graphite powder were added andmixed. Furthermore, 0.8 mass parts of zinc stearate as a forminglubricant was added and mixed with 100 mass parts of the mixed powder,and a raw powder was obtained. The obtained raw powder was compacted andsintered in the same way as in the example A-1, and samples Nos. D01 toD06 were formed. The simple wear tests and the corrosion tests wereperformed in the same way as in the example C-1 for these samples. Theresults of these tests are also shown in Table D-1.

TABLE D-1 Mixing ratio mass % Evaluation item Hard phase forming alloypowder Wear amount μm Corrosion Sample Iron alloy Compositions mass %Graphite Valve loss No. powder Co Fe Cr Mo Si powder sheet Valve Totalmg/cm² Notes D01 Balance 35.00 Balance 42.00 5.00 20.00 3.00 1.00 74 276 0.30 Comparative example D02 Balance 35.00 Balance 37.00 10.00 20.003.00 1.00 45 2 47 0.16 Practical example D03 Balance 35.00 Balance 27.0020.00 20.00 3.00 1.00 29 2 31 0.14 Practical example D04 Balance 35.00Balance 17.00 30.00 20.00 3.00 1.00 21 2 23 0.11 Practical example D05Balance 35.00 Balance 7.00 40.00 20.00 3.00 1.00 35 4 39 0.16 Practicalexample D06 Balance 35.00 Balance 2.00 45.00 20.00 3.00 1.00 69 20 890.26 Comparative example

According to Table D-1, the influence of the amount of Cr in the hardphase forming alloy powder (the amount of Cr in the hard phase) wasinvestigated. In the sample No. D01, the amount of Cr in the hard phaseforming alloy powder was insufficient, whereby the matrix of sinteredalloy was not sufficiently strengthened, and the wear amount of thevalve sheet was large. Moreover, since the amount of Cr wasinsufficient, the corrosion resistance was insufficient, and thecorrosion loss was also large. In the sample No. D02 in which the amountof Cr in the hard phase forming alloy powder was 10%, the wear amount ofthe valve sheet was remarkably decreased because the matrix wasstrengthened by Cr. Moreover, the corrosion loss was reduced becausecorrosion resistance was improved. When the amount of Cr in the hardphase forming alloy powder was not more than 30%, the wear amounts ofthe valve sheets were at low levels and the corrosion losses werereduced according to the increase in amount of Cr. In the sample No. D05in which the amount of Cr in the hard phase forming alloy powder was40%, the hardness of the hard phase forming alloy powder was increasedby the increase in the amount of Cr in the hard phase forming alloypowder, whereby compressibility of the raw powder was decreased, and thedensity of the green compact was decreased. As a result, the density ofthe sintered compact was decreased, whereby the wear amount of the valvesheet and the corrosion loss were increased, but these values weresufficiently small. Moreover, the wear amount of the valve was alsoincreased because the wear particles of the valve sheet eroded thevalve, but this value was small. However, in the sample No. D06 in whichthe amount of Cr in the hard phase forming alloy powder was greater than40%, this tendency was more remarkable, and therefore the total of thewear amounts and the corrosion loss were remarkably increased. Accordingto the above results, when the amount of Cr in the hard phase formingalloy powder (the amount of Cr in the hard phase) was 10 to 40%, thewear amounts of the valve sheet and the valve were small and thecorrosion loss of the sintered alloy was small.

Example D-2

The iron alloy powder (Fe-6.5% Co-1.5% Ni-1.5% Mo powder) used in theexample D-1, the hard phase forming alloy powder (Co-30% Cr-20% Mo-17%Fe-3% Si powder) used in the sample No. D04 in the example D-1, and agraphite powder were prepared. The ratio of the hard phase forming alloypowder were changed as shown in Table D-2, and these powders were addedand mixed. Furthermore, 0.8 mass parts of zinc stearate as a forminglubricant was added and mixed with 100 mass parts of the mixed powder,and a raw powder was obtained. The obtained raw powder was compacted andsintered in the same way as in the example A-1, and samples Nos. D07 toD11 were formed. The wear tests and the corrosion tests were performedin the same way as in the example C-1 for these samples. The results areshown in Table D-2 with the values of the sample No. D04 in the exampleD-1.

TABLE D-2 Mixing ratio mass % Hard phase Evaluation item forming Wearamount μm Corrosion Sample Iron alloy alloy Graphite Valve loss No.powder powder powder sheet Valve Total mg/cm² Notes D07 Balance 5.001.00 102 2 104 0.49 Comparative example D08 Balance 15.00 1.00 46 1 470.22 Practical example D09 Balance 25.00 1.00 25 2 27 0.16 Practicalexample D04 Balance 35.00 1.00 21 2 23 0.11 Practical example D10Balance 45.00 1.00 38 5 43 0.14 Practical example D11 Balance 55.00 1.0073 34 107 0.24 Comparative example

According to Table D-2, the influence of the amount of the hard phaseforming alloy powder (the amount of the hard phase dispersed in thematrix) was investigated. In the sample No. D07 in which the amount ofthe hard phase forming alloy powder was less than 15%, the wear amountof the valve sheet was large because the amount of the hard phase wasinsufficient and the plastic flow of the matrix could not be prevented.Moreover, the hard phase was insufficient, and Cr was not sufficientlydispersed from the hard phase to the matrix, whereby the corrosion losswas large. In the sample No. D08 in which the amount of the hard phaseforming alloy powder was 15%, wear resistance and corrosion resistanceof the matrix of the sintered alloy were improved by the hard phase, andthe wear amount of the valve sheet was remarkably decreased and thecorrosion loss was decreased. When the amount of the hard phase formingalloy powder was not more than 35%, the wear amount of the valve sheetand the corrosion loss were decreased according to the increase in theamount of the hard phase forming alloy powder. In the sample No. D10 inwhich the amount of the hard phase forming alloy powder was 45%,compressibility of the raw powder was decreased by the increase in theamount of the hard phase forming alloy powder, whereby the wear amountof the valve sheet and the corrosion loss were slightly increased, butthese were at low levels. On the other hand, in the sample No. D11 inwhich the amount of the hard phase forming alloy powder was greater than45%, the influence of the decrease of compressibility was remarkable,whereby the wear amount of the valve sheet was remarkably increased, andthe corrosion loss was increased. Moreover, the wear amount of the valvewas also remarkably increased because the wear particles of the valvesheet eroded the valve. According to the above results, when the amountof the hard phase forming alloy powder (the amount of the hard phasedispersed in the matrix) was 15 to 45%, the wear amounts of the valvesheet and the valve were small.

Example D-3

An iron alloy powder as shown in Table D-3, a graphite powder, and thehard phase forming alloy powder (Co-30% Cr-20% Mo-17% Fe-3% Si powder)used in the sample No. D04 in the example D-1 were prepared. In the ironalloy powder, the amount of Co was different from that of the iron alloypowder used in the example D-1. The iron alloy powder, 35% of the hardphase forming alloy powder, and 1% of the graphite powder were added andmixed. Furthermore, 0.8 mass parts of zinc stearate as a forminglubricant was added and mixed with 100 mass parts of the mixed powder.The obtained raw powder was compacted and sintered in the same way as inthe example A-1, and samples Nos. D12 to D16 were formed. The wear testsand the corrosion tests were performed in the same way as in the exampleC-1 for these samples. The results are shown in Table D-3 with thevalues of the sample No. D04 in the example D-1.

TABLE D-3 Mixing ratio mass % Hard phase Evaluation item Iron alloypowder forming Wear amount μm Corrosion Sample compositions mass % alloyGraphite Valve loss No. Fe Co Ni Mo powder powder sheet Valve Totalmg/cm² Notes D12 Balance Balance 1.00 1.50 1.50 35.00 1.00 89 1 90 0.17Comparative example D13 Balance Balance 3.00 1.50 1.50 35.00 1.00 42 244 0.15 Practical example D14 Balance Balance 5.00 1.50 1.50 35.00 1.0030 2 32 0.11 Practical example D04 Balance Balance 6.50 1.50 1.50 35.001.00 21 2 23 0.10 Practical example D15 Balance Balance 8.00 1.50 1.5035.00 1.00 23 2 25 0.12 Practical example D16 Balance Balance 10.00 1.501.50 35.00 1.00 66 4 70 0.23 Comparative example

According to Table D-3, the influence of the amount of Co in the ironalloy powder was investigated. In the sample No. D12 in which the amountof Co was less than 3%, the wear amount of the valve sheet and thecorrosion loss were large because strength and heat resistance of the Fematrix were not sufficiently improved by Co. In the sample No. D13 inwhich the amount of Co in the iron alloy powder was 3%, the wear amountof the valve sheet was remarkably decreased because the Fe matrix wasstrengthened by Co and heat resistance was improved by Co, and thecorrosion loss was decreased because corrosion resistance of the Fematrix was improved. When the amount of Co in the iron alloy powder wasnot more than 6.5%, the wear amount of the valve sheet and the corrosionloss were decreased according to the increase in the amount of Co in theiron alloy powder. In the sample No. D15 in which the amount of Co inthe iron alloy powder was 8%, compressibility of the raw powder wasdecreased by the increase in the hardness of the iron alloy powder,whereby the density of the green compact was decreased. As a result, thedensity of the sintered compact was decreased, whereby the wear amountof the valve sheet and the corrosion loss were slightly increased, butthese were at low levels. On the other hand, in the sample No. D16 inwhich the amount of Co in the iron alloy powder was greater than 8%, theinfluence of the increase in the hardness of the iron alloy powder wasremarkable, and the density of the sintered compact was remarkablydecreased, whereby the wear amount of the valve sheet and the corrosionloss were remarkably increased. According to the above results, when theamount of Co in the iron alloy powder was 3 to 8%, the wear amount ofthe valve sheet was small and the corrosion loss was reduced.

Example D-4

The iron alloy powder (Fe-6.5% Co-1.5% Ni-1.5% Mo powder) used in theexample D-1, the hard phase forming alloy powder (Co-30% Cr-20% Mo-17%Fe-3% Si powder) used in the sample No. D04 in the example D-1, and agraphite powder were prepared. The ratio of the graphite powder waschanged as shown in Table D-4, and these powders were added and mixed.Furthermore, 0.8 mass parts of zinc stearate as a forming lubricant wasadded and mixed 100 mass parts of the mixed powder, and a raw powder wasmixed. The obtained raw powder was compacted and sintered in the sameway as in the example A-1, and samples Nos. D17 to D22 were formed. Thewear tests were performed in the same way as in the example C-1 forthese samples. The results are shown in Table D-4 with the values of thesample No. D04 in the example D-1.

TABLE D-4 Mixing ratio mass % Hard phase Evaluation item forming Wearamount μm Iron alloy alloy Graphite Valve Sample No. powder powderpowder sheet Valve Total Notes D17 Balance 35.00 0.30 121 2 123Comparative example D18 Balance 35.00 0.50 55 2 57 Practical example D19Balance 35.00 0.80 25 2 27 Practical example C04 Balance 35.00 1.00 21 223 Practical example D20 Balance 35.00 1.20 25 3 28 Practical exampleD21 Balance 35.00 1.50 48 7 55 Practical example D22 Balance 35.00 1.8090 41 131 Comparative example

According to Table D-4, the influence of the amount of the graphitepowder (the amount of C in the overall composition) was investigated. Inthe sample No. D17 in which the amount of the graphite powder was lessthan 0.5%, the wear amount of the valve sheet was large because Fematrix of the sintered alloy was not sufficiently strengthened. In thesample No. D18 in which the amount of the graphite powder was 0.5%, thewear amount of the valve sheet was remarkably decreased because the Fematrix of the sintered alloy was strengthened. When the amount of thegraphite powder was not more than 1.0%, the wear amount of the valvesheet was decreased according to the increase in the amount of thegraphite powder. In the sample in which the amount of the graphitepowder was 1.2 to 1.5%, the wear amount of the valve sheet was increasedand the wear amount of the valve was slightly increased because the Fematrix of the sintered alloy was hardened and embrittled. In this case,the total of the wear amounts was not a problem in practical use. On theother hand, in the sample No. D22 in which the amount of the graphitepowder was greater than 1.5%, this tendency was more remarkable, andtherefore the wear amount of the valve sheet was remarkably increased.Moreover, the wear amount of the valve was also remarkably increasedbecause the wear particles of the valve sheet eroded the valve.According to the above results, when the amount of the graphite powder(the amount of C in the overall composition) was 0.5 to 1.5%, the wearamounts of the valve sheet and the valve were small.

Example D-5

The iron alloy powder (Fe-6.5% Co-1.5% Ni-1.5% Mo powder) used in theexample D-1, a graphite powder, and a hard phase forming alloy powder asshown in Table D-5 were prepared. The hard phase forming alloy powderhad a composition in which a ratio of Co and Fe was different from thatof the hard phase forming alloy powder (Co-30% Cr-20% Mo-17% Fe-3% Sipowder) used in the sample No. D04 in the example D-1. The iron alloypowder, 35% of the hard phase forming alloy powder and 1% of thegraphite powder were added and mixed. Furthermore, 0.8 mass parts ofzinc stearate as a forming lubricant was added and mixed with 100 massparts of the mixed powder, and a raw powder was obtained. The obtainedraw powder was compacted and sintered in the same way as in the exampleA-1, and samples Nos. D23 to D28 were formed. The wear tests wereperformed in the same way as in the example C-1 for these samples. Theresults are shown in Table D-5 with the values of the sample No. D04 inthe example D-1.

TABLE D-5 Mixing ratio mass % Evaluation item Hard phase forming alloypowder Wear amount μm Sample Iron alloy Compositions mass %Substitutional Graphite Valve No. powder Co Fe Cr Mo Si ratio of Fepowder sheet Valve Total Notes D23 Balance 35.00 Balance 0.00 30.0020.00 3.00 0.00 1.00 15 2 17 Practical example D24 Balance 35.00 Balance7.00 30.00 20.00 3.00 14.90 1.00 18 2 20 Practical example D04 Balance35.00 Balance 17.00 30.00 20.00 3.00 36.20 1.00 21 2 23 Practicalexample D25 Balance 35.00 Balance 28.00 30.00 20.00 3.00 59.60 1.00 24 226 Practical example D26 Balance 35.00 Balance 37.50 30.00 20.00 3.0079.80 1.00 40 3 43 Practical example D27 Balance 35.00 Balance 42.0030.00 20.00 3.00 89.40 1.00 71 4 75 Practical example D28 Balance 35.00Balance 47.00 30.00 20.00 3.00 100.00 1.00 102 9 111 Comparative example

According to Table D-5, when Co in the hard phase forming alloy powderwas substituted by Fe, the influence of the substitutional ratio of Fewas investigated. In the sample No. D23 in which Co in the hard phaseforming alloy powder was not substituted by Fe, the wear amounts werethe least among the above examples D and wear resistance was good. WhenCo in the hard phase forming alloy powder was substituted by Fe and thesubstitutional ratio of Fe was increased, the wear amounts wereincreased. In this case, when the substitutional ratio of Fe was notmore than 80% (samples Nos. D04 and D24 to D26), the wear amounts werenot a problem in practical use. However, in the samples Nos. D27 and D28in which the substitutional ratio of Fe was more than 80%, the wearamounts were remarkably increased, because the effect of Co wasinsufficient. According to the above results, although Co in the hardphase forming alloy powder could be substituted by Fe, thesubstitutional ratio of Fe should be not more than 80%. Thesubstitutional ratio of Fe is preferably not more than 60%.

Example D-6

The iron alloy powder (Fe-6.5% Co-1.5% Ni-1.5% Mo powder) used in theexample D-1, a graphite powder, and a hard phase forming alloy powder asshown in Table D-6 were prepared. The hard phase forming alloy powderwas formed by adding different amount of Mn in the hard phase formingalloy powder (Co-30% Cr-20% Mo-17% Fe-3% Si powder) used in the sampleNo. D04 in the example D-1. The iron alloy powder, 35% of the hard phaseforming alloy powder and 1% of the graphite powder were added and mixed.Furthermore, 0.8 mass parts of zinc stearate as a forming lubricant wasadded and mixed with 100 mass parts of the mixed powder, and a rawpowder was obtained. The obtained raw powder was compacted and sinteredin the same way as in the example A-1, and samples Nos. D29 to D32 wereformed. The wear tests were performed in the same way as in the exampleC-1 for these samples. The results are shown in Table D-6 with thevalues of the sample No. D04 in the example D-1.

TABLE D-6 Mixing ratio mass % Evaluation item Hard phase forming alloypowder Wear amount μm Sample Iron alloy Compositions mass % GraphiteValve No. powder Co Fe Cr Mo Si Mn powder sheet Valve Total Notes D04Balance 35.00 Balance 17.00 30.00 20.00 3.00 — 1.00 21 2 23 Practicalexample D29 Balance 35.00 Balance 17.00 30.00 20.00 3.00 1.00 1.00 19 221 Practical example D30 Balance 35.00 Balance 17.00 30.00 20.00 3.003.00 1.00 16 3 19 Practical example D31 Balance 35.00 Balance 17.0030.00 20.00 3.00 5.00 1.00 20 9 29 Practical example D32 Balance 35.00Balance 17.00 30.00 20.00 3.00 7.00 1.00 38 45 83 Comparative example

According to Table D-6, the effect of Mn added in the hard phase formingalloy powder (the hard phase) was investigated. In the samples Nos. D29to D31 in which the amount of Mn in the hard phase forming alloy powderwas not more than 5%, the alloy matrix of the hard phase wasstrengthened by Mn, whereby the wear amounts of valve sheets were lessthan that of the sample No. D04 in which Mn in the hard phase formingalloy powder was not added. On the other hand, the wear amounts of thevalves were slightly increased according to the increase in the amountof Mn, because the hard phase was strengthened. In the sample No. D32 inwhich the amount of Mn in the hard phase forming alloy powder wasgreater than 5%, the hard phase forming alloy powder was hardened, andcompressibility of the raw powder was remarkably decreased, whereby thewear amount of the valve sheet was remarkably increased. Moreover, thewear amount of the valve was also remarkably increased because the wearparticles of the valve sheet eroded the valve. According to the aboveresults, although wear resistance could be further improved by adding Mnin the hard phase forming alloy powder, the amount of Mn in the hardphase forming alloy powder should be not more than 5%.

Example D-7

The iron alloy powder (Fe-6.5% Co-1.5% Ni-1.5% Mo powder) used in theexample D-1, the hard phase forming alloy powder (Co-30% Cr-20% Mo-17%Fe-3% Si powder) used in the sample No. D04 in the example D-1, agraphite powder, and a nickel powder were prepared. The iron alloypowder, 35% of the hard phase forming alloy powder, 1% of the graphitepowder, and a ratio shown in Table D-7 of the nickel powder were addedand mixed. Furthermore, 0.8 mass parts of zinc stearate as a forminglubricant was added and mixed with 100 mass parts of the mixed powder,and a raw powder was obtained. The obtained raw powder was compacted andsintered in the same way as in the example A-1, and samples Nos. D33 toD39 were formed. The wear tests were performed in the same way as in theexample C-1 for these samples. The results are shown in Table D-7 withthe values of the sample No. D04 in the example D-1.

TABLE D-7 Mixing ratio mass % Hard phase Evaluation item forming Wearamount μm Sample Iron alloy alloy Graphite Nickel Valve No. powderpowder powder powder sheet Valve Total Notes D04 Balance 35.00 1.00 0.0021 2 23 Practical example D33 Balance 35.00 1.00 0.10 20 2 22 Practicalexample D34 Balance 35.00 1.00 1.00 18 2 20 Practical example D35Balance 35.00 1.00 2.00 16 2 18 Practical example D36 Balance 35.00 1.003.00 17 2 19 Practical example D37 Balance 35.00 1.00 4.00 18 2 20Practical example D38 Balance 35.00 1.00 5.00 20 3 23 Practical exampleD39 Balance 35.00 1.00 7.00 49 8 57 Comparative example

According to Table D-7, compared with the sample No. D04 in which thenickel powder was not added to the raw powder and Ni was not added inthe matrix, in the samples Nos. D33 to D38 in which the nickel powderwas added at not more than 5%, the wear amount of the valve sheet wasdecreased and the total of the wear amounts was decreased. In the sampleNo. D39 in which the amount of the nickel powder was greater than 5%, alarge amount of Ni-rich austenite having low wear resistance was formedand remained in the matrix, whereby wear resistance of the valve sheetwas decreased and the wear amount of the valve sheet was increased.Moreover, the amount of the hard martensite was increased, and theerosion of the valve (the mating material) was increased, whereby thewear amount of the valve was increased and the total of the wear amountswas remarkably increased. Accordingly, although wear resistance wasimproved by adding the nickel powder, the amount of the nickel powdershould be not more than 5.0%.

Example E Fe—Ni—Mo—C Alloy Matrix Example E-1

An iron alloy powder consisting of 2% of Ni, 1% of Mo, 0.5% of Cr, 0.3%of Mn, and the balance of Fe and inevitable impurities, a hard phaseforming alloy powder shown in Table E-1, and a graphite powder wereprepared. The iron alloy powder, 35% of the hard phase forming alloypowder, and 1% of the graphite powder were added and mixed. Furthermore,0.8 mass parts of zinc stearate as a forming lubricant was added andmixed with 100 mass parts of the mixed powder, and a raw powder wasobtained. The obtained raw powder was compacted and sintered in the sameway as in the example A-1, and samples Nos. E01 to E06 were formed. Thesimple wear tests and the corrosion tests were performed in the same wayas in the example C-1 for these samples. The results of these tests arealso shown in Table E-1.

TABLE E-1 Mixing ratio mass % Evaluation item Hard phase forming alloypowder Wear amount μm Corrosion Sample Iron alloy Compositions mass %Graphite Valve loss No. powder Co Fe Cr Mo Si powder sheet Valve Totalmg/cm² Notes E01 Balance 35.00 Balance 42.00 5.00 20.00 3.00 1.00 92 496 0.31 Comparative example E02 Balance 35.00 Balance 37.00 10.00 20.003.00 1.00 55 4 59 0.15 Practical example E03 Balance 35.00 Balance 27.0020.00 20.00 3.00 1.00 37 4 41 0.14 Practical example E04 Balance 35.00Balance 17.00 30.00 20.00 3.00 1.00 27 4 31 0.11 Practical example E05Balance 35.00 Balance 7.00 40.00 20.00 3.00 1.00 42 7 49 0.15 Practicalexample E06 Balance 35.00 Balance 2.00 45.00 20.00 3.00 1.00 79 24 1030.32 Comparative example

According to Table E-1, the influence of the amount of Cr in the hardphase forming alloy powder (the amount of Cr in the hard phase) wasinvestigated. In the sample No. E01, the amount of Cr in the hard phaseforming alloy powder was insufficient, whereby the matrix of sinteredalloy was not sufficiently strengthened, and the wear amount of thevalve sheet was large. Moreover, since the amount of Cr wasinsufficient, corrosion resistance was insufficient, and the corrosionloss was also large. In the sample No. E02 in which the amount of Cr inthe hard phase forming alloy powder was 10%, the wear amount of thevalve sheet was remarkably decreased because the matrix was strengthenedby Cr. Moreover, the corrosion loss was reduced because corrosionresistance was improved by Cr. When the amount of Cr in the hard phaseforming alloy powder was not more than 30%, the wear amounts of thevalve sheets were low values and the corrosion losses were reducedaccording to the increase in the amount of Cr. In the sample No. E05 inwhich the amount of Cr in the hard phase forming alloy powder was 40%,the hardness of the hard phase forming alloy powder was increased by theincrease in the amount of Cr in the hard phase forming alloy powder,whereby compressibility of the raw powder was decreased, and the densityof the green compact was decreased. As a result, the density of thesintered compact was decreased, whereby the wear amount of the valvesheet and the corrosion loss were increased, but these values weresufficiently small. Moreover, the wear amount of the valve was alsoincreased because the wear particles of the valve sheet eroded thevalve, but this value was small. However, in the sample No. E06 in whichthe amount of Cr in the hard phase forming alloy powder was greater than40%, this tendency was more remarkable, and therefore the total of thewear amounts and the corrosion loss were remarkably increased. Accordingto the above results, when the amount of Cr in the hard phase formingalloy powder was 10 to 40%, the wear amounts of the valve sheet and thevalve were small and the corrosion losses of the sintered alloys weresmall.

Example E-2

The iron alloy powder (Fe-2% Ni-1% Mo-0.5% Cr-0.3% Mn powder) used inthe example E-1, the hard phase forming alloy powder (Co-30% Cr-20%Mo-17% Fe-3% Si powder) used in the sample No. E04 in the example E-1,and a graphite powder were prepared. The ratio of the hard phase formingalloy powder was changed as shown in Table E-2, and these powders wereadded and mixed. Furthermore, 0.8 mass parts of zinc stearate as aforming lubricant was added and mixed with 100 mass parts of the mixedpowder, and a raw powder was obtained. The obtained raw powder wascompacted and sintered in the same way as in the example A-1, andsamples Nos. E07 to E11 were formed. The wear tests and the corrosiontests were performed in the same way as in the example C-1 for thesesamples. The results are shown in Table E-2 with the values of thesample No. E04 in the example E-1.

TABLE E-2 Mixing ratio mass % Hard phase Evaluation item forming Wearamount μm Corrosion Sample Iron alloy alloy Graphite Valve loss No.powder powder powder sheet Valve Total mg/cm² Notes E07 Balance 5.001.00 110 2 112 0.51 Comparative example E08 Balance 15.00 1.00 53 3 560.26 Practical example E09 Balance 25.00 1.00 32 3 35 0.15 Practicalexample E10 Balance 35.00 1.00 27 4 31 0.11 Practical example E11Balance 45.00 1.00 45 6 51 0.18 Practical example E12 Balance 55.00 1.0086 45 131 0.45 Comparative example

According to Table E-2, the influence of the amount of the hard phaseforming alloy powder (the amount of the hard phase dispersed in thematrix) was investigated. In the sample No. E07 in which the amount ofthe hard phase forming alloy powder was less than 15%, the wear amountof the valve sheet was large because the amount of the hard phase wasinsufficient and the plastic flow of the matrix could not be prevented.Moreover, the hard phase was insufficient, and Cr was not sufficientlydispersed from the hard phase to the matrix, whereby the corrosion losswas large. In the sample No. E08 in which the amount of the hard phaseforming alloy powder was 15%, the wear amount of the valve sheet wasremarkably decreased and the corrosion loss was decreased because wearresistance and corrosion resistance of the matrix of the sintered alloyare improved by the hard phase. When the amount of the hard phaseforming alloy powder was not more than 35%, the wear amount of the valvesheet and the corrosion loss were decreased according to the increase inthe amount of the hard phase forming alloy powder. In the sample No. E10in which the amount of the hard phase forming alloy powder was 45%,compressibility of the raw powder was decreased by the increase in theamount of the hard phase forming alloy powder, whereby the wear amountof the valve sheet and the corrosion loss were slightly increased, butthese were at low levels. On the other hand, in the sample No. E11 inwhich the amount of the hard phase forming alloy powder was greater than45%, the influence of the decrease of compressibility was remarkable,whereby the wear amount of the valve sheet was remarkably increased andthe corrosion loss was increased. Moreover, the wear amount of the valvewas also remarkably increased because the wear particles of the valvesheet eroded the valve. According to the above results, when the amountof the hard phase forming alloy powder (the amount of the hard phasedispersed in the matrix) was 15 to 45%, the wear amounts of the valvesheet and the valve were small.

Example E-3

An iron alloy powder having a composition shown in Table E-3, the hardphase forming alloy powder (Co-30% Cr-20% Mo-17% Fe-3% Si powder) usedin the sample No. E04 in the example E-1, and a graphite powder wereprepared. The iron alloy powder, 35% of the hard phase forming alloypowder and 1% of the graphite powder were added and mixed. Furthermore,0.8 mass parts of zinc stearate as a forming lubricant was added andmixed with 100 mass parts of the mixed powder, and a raw powder wasobtained. The obtained raw powder was compacted and sintered in the sameway as in the example A-1, and samples Nos. E12 to E20 were formed. Thewear tests and the corrosion tests were performed in the same way as inthe example C-1 for these samples. The results are shown in Table E-3with the values of the sample No. E04 in the example E-1.

TABLE E-3 Mixing ratio mass % Hard phase Evaluation item Iron alloypowder forming Wear amount μm Sample Compositions mass % alloy GraphiteValve No. Fe Ni Cr Mo Mn powder powder sheet Valve Total Notes E12Balance Balance 0.00 0.50 1.00 0.30 35.00 1.00 85 3 88 Comparativeexample E13 Balance Balance 1.00 0.50 1.00 0.30 35.00 1.00 40 4 44Practical example E04 Balance Balance 2.00 0.50 1.00 0.30 35.00 1.00 274 31 Practical example E14 Balance Balance 3.00 0.50 1.00 0.30 35.001.00 33 5 38 Practical example E15 Balance Balance 5.00 0.50 1.00 0.3035.00 1.00 59 13 72 Comparative example E16 Balance Balance 2.00 0.001.00 0.30 35.00 1.00 62 2 64 Comparative example E17 Balance Balance2.00 0.10 1.00 0.30 35.00 1.00 41 2 43 Practical example E18 BalanceBalance 2.00 0.30 1.00 0.30 35.00 1.00 31 3 34 Practical example E04Balance Balance 2.00 0.50 1.00 0.30 35.00 1.00 27 4 31 Practical exampleE19 Balance Balance 2.00 1.00 1.00 0.30 35.00 1.00 35 5 40 Practicalexample E20 Balance Balance 2.00 1.50 1.00 0.30 35.00 1.00 67 14 81Comparative example

According to samples Nos. E04 and E12 to E15 in Table E-3, the influenceof the amount of Ni in the iron alloy powder was investigated. In thesample No. E12 in which Ni was not added in the iron alloy powder, thewear amount of the valve sheet and the corrosion loss were large becausethe Fe matrix of the sintered alloy was not strengthened. In the samplesNos. E13, E04, and E14 in which the amount of Ni in the iron alloypowder was 1 to 3%, strength and corrosion resistance of the Fe matrixwere improved by Ni, the wear amount of the valve sheet was remarkablydecreased, and the corrosion loss was decreased. In the sample No. E15in which the amount of Ni in the iron alloy powder was greater than 3%,compressibility of the raw powder was decreased by the increase in thehardness of the iron alloy powder, whereby the density of the compactwas decreased. As a result, the density of the sintered compact wasdecreased, whereby the wear amount of the valve sheet and the corrosionloss were remarkably increased. According to the above results, when theamount of Ni in the iron alloy powder was 1 to 3%, the wear amount ofthe valve sheet was small and the corrosion loss was reduced.

According to samples Nos. E04 and E16 to E20 in Table E-3, the influenceof the amount of Cr in the iron alloy powder was investigated. In thesample No. E16 in which Cr was not added in the iron alloy powder, thewear amount of the valve sheet and the corrosion loss were large becausethe Fe matrix of the sintered alloy was not strengthened. However, inthe samples Nos. E18, E04, and E19 in which the amount of Cr in the ironalloy powder was 0.1 to 1%, strength and corrosion resistance of the Fematrix were improved by Cr, whereby the wear amount of the valve sheetwas remarkably decreased, and the corrosion loss was decreased. In thesample No. E20 in which the amount of Cr in the iron alloy powder wasgreater than 1%, compressibility of the raw powder was decreased by theincrease in the hardness of the iron alloy powder, whereby the densityof the green compact was decreased. As a result, the density of thesintered compact was decreased, whereby the wear amount of the valvesheet and the corrosion loss were remarkably increased. According to theabove results, when the amount of Cr in the iron alloy powder was 0.1 to1%, the wear amount of the valve sheet was small and the corrosion losswas reduced.

Example E-4

The iron alloy powder (Fe-2% Ni-1% Mo-0.5% Cr-0.3% Mn powder) used inthe example E-1, the hard phase forming alloy powder (Co-30% Cr-20%Mo-17% Fe-3% Si powder) used in the sample No. E04 in the example E-1,and a graphite powder were prepared. The ratio of the graphite powderwas changed as shown in Table E-4, and these powders were added andmixed. Furthermore, 0.8 mass parts of zinc stearate as a forminglubricant was added and mixed with 100 mass parts of the mixed powder,and a raw powder was obtained. The obtained raw powder was compacted andsintered in the same way as in the example A-1, and samples Nos. E21 toE26 were formed. The wear tests were performed in the same way as in theexample C-1 for these samples. The results are shown in Table E-4 withthe values of the sample No. E04 in the example E-1.

TABLE E-4 Mixing ratio mass % Hard phase Evaluation item Sam- Ironforming Wear amount μm ple alloy alloy Graphite Valve No. powder powderpowder sheet Valve Total Notes E21 Balance 35.00 0.30 113 2 115Comparative example E22 Balance 35.00 0.50 54 3 57 Practical example E23Balance 35.00 0.80 32 4 36 Practical example E04 Balance 35.00 1.00 27 431 Practical example E24 Balance 35.00 1.20 32 5 37 Practical exampleE25 Balance 35.00 1.50 51 10 61 Practical example E26 Balance 35.00 1.80102 52 154 Comparative example

According to Table E-4, the influence of the amount of the graphitepowder (the amount of C in the overall composition) was investigated. Inthe sample No. E21 in which the amount of the graphite powder was lessthan 0.5%, the wear amount of the valve sheet was large because the Fematrix of the sintered alloy was not sufficiently strengthened. In thesample No. E22 in which the amount of the graphite powder was 0.5%, thewear amount of the valve sheet was remarkably decreased because the Fematrix of the sintered alloy was strengthened. When the amount of thegraphite powder was not more than 1.0%, the wear amount of the valvesheet was decreased according to the increase in the amount of thegraphite powder. In the samples in which the amount of the graphitepowder was 1.0 to 1.5%, the Fe matrix of the sintered alloy was hardenedand embrittled, whereby the wear amount of the valve sheet was increasedand the wear amount of the valve was slightly increased. In this case,the total of the wear amounts was not a problem in practical use. On theother hand, in the sample No. E26 in which the amount of the graphitepowder was greater than 1.5%, this tendency was more remarkable, andtherefore the wear amount of the valve sheet was remarkably increased.Moreover, the wear amount of the valve was also remarkably increasedbecause the wear particles of the valve sheet eroded the valve.According to the above results, when the amount of the graphite powder(the amount of C in the overall composition) was 0.5 to 1.5%, the wearamounts of the valve sheet and the valve were small.

Example E-5

The iron alloy powder (Fe-2% Ni-1% Mo-0.5% Cr-0.3% Mn powder) used inthe example E-1, a graphite powder, and a hard phase forming alloypowder as shown in Table E-5 were prepared. The hard phase forming alloypowder had a composition in which a ratio of Co and Fe was differentfrom that of the hard phase forming alloy powder (Co-30% Cr-20% Mo-17%Fe-3% Si powder) used in the sample No. E04 in the example E-1. The ironalloy powder, 35% of the hard phase forming alloy powder, and 1% of thegraphite powder were added and mixed. Furthermore, 0.8 mass parts ofzinc stearate as a forming lubricant was added and mixed with 100 massparts of the mixed powder, and a raw powder was obtained. The obtainedraw powder was compacted and sintered in the same way as in the exampleA-1, and samples Nos. E27 to E32 were formed. The wear tests wereperformed in the same way as in the example C-1 for these samples. Theresults are shown in Table E-5 with the values of the sample No. E04 inthe example E-1.

TABLE E-5 Mixing ratio mass % Evaluation item Hard phase forming alloypowder Wear amount μm Sample Iron alloy Compositions mass %Substitutional Graphite Valve No. powder Co Fe Cr Mo Si ratio of Fepowder sheet Valve Total Notes E27 Balance 35.00 Balance 0.00 30.0020.00 3.00 0.00 1.00 19 3 22 Practical example E28 Balance 35.00 Balance7.00 30.00 20.00 3.00 14.90 1.00 23 3 26 Practical example E04 Balance35.00 Balance 17.00 30.00 20.00 3.00 36.20 1.00 27 4 31 Practicalexample E29 Balance 35.00 Balance 28.00 30.00 20.00 3.00 59.60 1.00 31 435 Practical example E30 Balance 35.00 Balance 37.50 30.00 20.00 3.0079.80 1.00 49 4 53 Practical example E31 Balance 35.00 Balance 42.0030.00 20.00 3.00 89.40 1.00 88 6 94 Practical example E32 Balance 35.00Balance 47.00 30.00 20.00 3.00 100.00 1.00 129 12 141 Comparativeexample

According to Table E-5, when Co in the hard phase forming alloy powderwas substituted by Fe, the influence of the substitutional ratio of Fewas investigated. In the sample No. E27 in which Co in the hard phaseforming alloy powder was not substituted by Fe, the wear amounts werethe least among the above examples E and wear resistance was good. WhenCo in the hard phase forming alloy powder was substituted by Fe and thesubstitutional ratio of Fe was increased, the wear amounts wereincreased. In this case, when the substitutional ratio of Fe was notmore than 80% (samples Nos. E04 and E28 to E30), the wear amounts werenot a problem in practical use. However, in the samples Nos. E31 and E32in which the substitutional ratio of Fe was more than 80%, the wearamounts were remarkably increased, because the effect of Co wasinsufficient. According to the above results, although Co in the hardphase forming alloy powder could be substituted by Fe, thesubstitutional ratio of Fe should be not more than 80%. Furthermore, thesubstitutional ratio of Fe was preferably not more than 60%.

Example E-6

The iron alloy powder (Fe-2% Ni-1% Mo-0.5% Cr-0.3% Mn powder) used inthe example E-1, a graphite powder, and a hard phase forming alloypowder as shown in Table E-6 were prepared. The hard phase forming alloypowder was formed by adding different amount of Mn in the hard phaseforming alloy powder (Co-30% Cr-20% Mo-17% Fe-3% Si powder) used in thesample No. E04 in the example E-1. The iron alloy powder, 35% of thehard phase forming alloy powder, and 1% of the graphite powder wereadded and mixed. Furthermore, 0.8 mass parts of zinc stearate as aforming lubricant was added and mixed with 100 mass parts of the mixedpowder, and a raw powder was obtained. The obtained raw powder wascompacted and sintered in the same way as in the example A-1, andsamples Nos. E33 to E36 were formed. The wear tests were performed inthe same way as in the example C-1 for these samples. The results areshown in Table E-6 with the values of the sample No. E04 in the exampleE-1.

TABLE E-6 Mixing ratio mass % Evaluation item Hard phase forming alloypowder Wear amount μm Sample Iron alloy Composition mass % GraphiteValve No. powder Co Fe Cr Mo Si Mn powder sheet Valve Total Notes E04Balance 35.00 Balance 17.00 30.00 20.00 3.00 — 1.00 27 4 31 Practicalexample E33 Balance 35.00 Balance 17.00 30.00 20.00 3.00 1.00 1.00 24 428 Practical example E34 Balance 35.00 Balance 17.00 30.00 20.00 3.003.00 1.00 22 5 27 Practical example E35 Balance 35.00 Balance 17.0030.00 20.00 3.00 5.00 1.00 24 12 36 Practical example E36 Balance 35.00Balance 17.00 30.00 20.00 3.00 7.00 1.00 47 50 97 Comparative example

According to Table E-6, the effect of Mn in the hard phase forming alloypowder (the hard phase) was investigated. In the samples Nos. D33 to D35in which the amount of Mn in the hard phase forming alloy powder was notmore than 5%, the alloy matrix of the hard phase was strengthened by Mn,whereby the wear amounts of the valve sheets were less than that of thesample No. E04 in which Mn was not added in the hard phase forming alloypowder. On the other hand, the wear amounts of the valves were slightlyincreased according to the increase in the amount of Mn, because thehard phase was strengthened. In the sample No. E36 in which the amountof Mn in the hard phase forming alloy powder was greater than 5%, thehard phase forming alloy powder was hardened, and compressibility of theraw powder was remarkably decreased, whereby the wear amount of thevalve sheet was remarkably increased. Moreover, the wear amount of thevalve was also remarkably increased because the wear particles of thevalve sheet eroded the valve. According to the above results, althoughwear resistance could be further improved by adding Mn in the hard phaseforming alloy powder, the amount of Mn in the hard phase forming alloypowder should be not more than 5%.

Example E-7

The iron alloy powder (Fe-2% Ni-1% Mo-0.5% Cr-0.3% Mn powder) used inthe example E-1, the hard phase forming alloy powder (Co-30% Cr-20%Mo-17% Fe-3% Si powder) used in the sample No. E04 in the example E-1, agraphite powder, and a nickel powder were prepared. The iron alloypowder, 35% of the hard phase forming alloy powder, 1% of the graphitepowder, and a ratio shown in Table E-7 of the nickel powder were addedand mixed. Furthermore, 0.8 mass parts of zinc stearate as a forminglubricant was added and mixed with 100 mass parts of the mixed powder,and a raw powder was obtained. The obtained raw powder was compacted andsintered in the same way as in the example A-1, and samples Nos. E37 toE43 were formed. The wear tests were performed in the same way as in theexample C-1 for these samples. The results are shown in Table E-7 withthe values of the sample No. E04 in the example E-1.

TABLE E-7 Mixing ratio mass % Evaluation item Hard phase Wear amount μmSample Iron alloy forming Graphite Nickel Valve No. powder alloy powderpowder powder sheet Valve Total Notes E04 Balance 35.00 1.00 0.00 27 431 Practical example E37 Balance 35.00 1.00 0.10 25 4 29 Practicalexample E38 Balance 35.00 1.00 1.00 24 4 28 Practical example E39Balance 35.00 1.00 2.00 22 4 26 Practical example E40 Balance 35.00 1.003.00 21 4 25 Practical example E41 Balance 35.00 1.00 4.00 23 5 28Practical example E42 Balance 35.00 1.00 5.00 25 6 31 Practical exampleE43 Balance 35.00 1.00 7.00 75 10 85 Comparative example

According to Table E-7, compared with the sample No. E04 in which thenickel powder was not added to the raw powder and Ni was not added inthe matrix, in the samples Nos. E37 to E42 in which the nickel powderwas added at not more than 5%, the wear amount of the valve sheet wasdecreased and the total of the wear amounts were decreased. In thesample No. E43 in which the amount of the nickel powder was greater than5%, a large amount of Ni-rich austenite having low wear resistance wasformed and remained in the matrix, whereby wear resistance of the valvesheet was decreased and the wear amount of the valve sheet wasincreased. Moreover, the amount of hard martensite was increased, andthe erosion of the valve (the mating material) was increased, wherebythe wear amount of the valve was increased and the total of the wearamount was remarkably increased. Accordingly, although wear resistancewas improved by adding the nickel powder, the amount of the nickelpowder should be not more than 5.0%.

Example E-8

The iron alloy powder (Fe-2% Ni-1% Mo-0.5% Cr-0.3% Mn powder) used inthe example E-1, the hard phase forming alloy powder (Co-30% Cr-20%Mo-17% Fe-3% Si powder) used in the sample No. E04 in the example E-1, agraphite powder, and a copper powder were prepared. The iron alloypowder, 35% of the hard phase forming alloy powder, 1% of the graphitepowder, and a ratio shown in Table E-8 of the copper powder were addedand mixed. Furthermore, 0.8 mass parts of zinc stearate as a forminglubricant was added and mixed with 100 mass parts of the mixed powder,and a raw powder was obtained. The obtained raw powder was compacted andsintered in the same way as in the example A-1, and samples Nos. E44 toE50 were formed. The wear tests were performed in the same way as in theexample C-1 for these samples. The results are shown in Table E-8 withthe values of the sample No. E04 in the example E-1.

TABLE E-8 Mixing ratio mass % Evaluation item Hard phase Wear amount μmSample Iron alloy forming Graphite Copper Valve No. powder alloy powderpowder powder sheet Valve Total Notes E04 Balance 35.00 1.00 0.00 27 431 Practical example E44 Balance 35.00 1.00 0.10 25 4 29 Practicalexample E45 Balance 35.00 1.00 1.00 23 5 28 Practical example E46Balance 35.00 1.00 2.00 22 5 27 Practical example E47 Balance 35.00 1.003.00 22 5 27 Practical example E48 Balance 35.00 1.00 4.00 23 6 29Practical example E49 Balance 35.00 1.00 5.00 24 7 31 Practical exampleE50 Balance 35.00 1.00 7.00 53 46 99 Comparative example

According to Table E-8, compared with the sample No. E04 in which thecopper powder was not added to the raw powder and Cu was not added inthe matrix, in the samples Nos. E44 to E49 in which the copper powderwas added at not more than 5%, the wear amount of the valve sheet wasdecreased and the total of the wear amounts was decreased. In the sampleNo. E50 in which the amount of the copper powder was greater than 5%, apart of Cu was not solid-solved in the matrix, and Cu phase wasdispersed in the matrix, whereby the strength of the matrix wasdecreased, and the wear amount of the valve sheet was increased.Moreover, the amount of hard martensite was increased, and the erosionof valve (the mating material) was increased, whereby the wear amount ofthe valve was increased and the total of the wear amounts was remarkablyincreased. Accordingly, although wear resistance was improved by addingthe copper powder, the amount of the copper powder should be not morethan 5.0%.

Example F Fe—Mo—C Alloy Matrix Example F-1

An iron alloy powder consisting of 3% of Mo and the balance of Fe andinevitable impurities, a hard phase forming alloy powder shown in TableF-1, and a graphite powder were prepared. The iron alloy powder, 35% ofthe hard phase forming alloy powder, and 1% of the graphite powder wereadded and mixed. Furthermore, 0.8 mass parts of zinc stearate as aforming lubricant was added and mixed with 100 mass parts of the mixedpowder, and a raw powder was obtained. The obtained raw powder wascompacted and sintered in the same way as in the example A-1, andsamples Nos. F01 to F06 were formed. The simple wear tests and thecorrosion tests were performed in the same way as in the example C-1 forthese samples. The results of these tests are also shown in Table F-1.

TABLE F-1 Mixing ratio mass % Evaluation item Hard phase forming alloypowder Wear amount μm Corrosion Sample Iron alloy Composition mass %Graphite Valve loss No. powder Co Fe Cr Mo Si powder sheet Valve Totalmg/cm² Notes F01 Balance 35.00 Balance 42.00 5.00 20.00 3.00 1.00 63 568 0.28 Comparative example F02 Balance 35.00 Balance 37.00 10.00 20.003.00 1.00 37 5 42 0.14 Practical example F03 Balance 35.00 Balance 27.0020.00 20.00 3.00 1.00 25 5 30 0.11 Practical example F04 Balance 35.00Balance 17.00 30.00 20.00 3.00 1.00 18 5 23 0.08 Practical example F05Balance 35.00 Balance 7.00 40.00 20.00 3.00 1.00 28 7 35 0.14 Practicalexample F06 Balance 35.00 Balance 2.00 45.00 20.00 3.00 1.00 55 26 810.20 Comparative example

According to Table F-1, the influence of the amount of Cr in the hardphase forming alloy powder (the amount of Cr in the hard phase) wasinvestigated. In the sample No. F01, the amount of Cr in the hard phaseforming alloy powder was insufficient, whereby the matrix of sinteredalloy was not sufficiently strengthened, and the wear amount of thevalve sheet was large. Moreover, the amount of Cr was insufficient,whereby corrosion resistance was insufficient, and the corrosion losswas also large. In the sample No. F02 in which the amount of Cr in thehard phase forming alloy powder was 10%, the wear amount of the valvesheet was remarkably decreased because the matrix was strengthened byCr. Moreover, the corrosion loss was reduced because corrosionresistance was improved by Cr. When the amount of Cr in the hard phaseforming alloy powder was not more than 30%, the wear amounts of thevalve sheets were at low levels and the corrosion losses were reducedaccording to the increase in the amount of Cr. In the sample No. F05 inwhich the amount of Cr in the hard phase forming alloy powder was 40%,the hardness of the hard phase forming alloy powder was increased by theincrease in the amount of Cr in the hard phase forming alloy powder,whereby compressibility of the raw powder was decreased, and the densityof the green compact was decreased. As a result, the density of thesintered compact was decreased, whereby the wear amount of the valvesheet and the corrosion loss was increased, but these values weresufficiently small. Moreover, the wear particles of the valve sheeteroded the valve, and the wear amount of the valve was also increased,but this value was small. However, in the sample No. F06 in which theamount of Cr in the hard phase forming alloy powder was greater than40%, this tendency was more remarkable, and therefore the total of thewear amounts and the corrosion loss were remarkably increased. Accordingto the above results, when the amount of Cr in the hard phase formingalloy powder was 10 to 40%, the wear amounts of the valve sheet and thevalve were small and the corrosion losses of the sintered alloys weresmall.

Example F-2

The iron alloy powder (Fe-3% Mo powder) used in the example F-1, thehard phase forming alloy powder (Co-30% Cr-20% Mo-17% Fe-3% Si powder)used in the sample No. F04 in the example F-1, and a graphite powderwere prepared. The ratio of the hard phase forming alloy powder waschanged as shown in Table F-2, and these powders were added and mixed.Furthermore, 0.8 mass parts of zinc stearate as a forming lubricant wasadded and mixed with 100 mass parts of the mixed powder, and a rawpowder was obtained. The obtained raw powder was compacted and sinteredin the same way as in the example A-1, and samples Nos. F07 to F11 wereformed. The wear tests and the corrosion tests were performed in thesame way as in the example C-1 for these samples. The results are shownin Table F-2 with the values of the sample No. F04 in the example F-1.

TABLE F-2 Mixing ratio mass % Evaluation item Hard phase Wear amount μmCorrosion Sample Iron alloy forming Graphite Valve loss No. powder alloypowder powder sheet Valve Total mg/cm² Notes F07 Balance 5.00 1.00 72 274 0.46 Comparative example F08 Balance 15.00 1.00 35 4 39 0.18Practical example F09 Balance 25.00 1.00 21 5 26 0.13 Practical exampleF04 Balance 35.00 1.00 18 5 23 0.08 Practical example F10 Balance 45.001.00 29 7 36 0.15 Practical example F11 Balance 55.00 1.00 54 40 94 0.26Comparative example

According to Table F-2, the influence of the amount of the hard phaseforming alloy powder (the amount of the hard phase dispersed in thematrix) was investigated. In the sample No. F07 in which the amount ofthe hard phase forming alloy powder was less than 15%, the wear amountof the valve sheet was large because the amount of the hard phase wasinsufficient and the plastic flow of the matrix could not be prevented.Moreover, the hard phase was insufficient, and Cr was not sufficientlydispersed from the hard phase to the matrix, whereby the corrosion losswas large. In the sample No. F08 in which the amount of the hard phaseforming alloy powder was 15%, the wear amount of the valve sheet wasremarkably decreased and the corrosion loss was decreased because thewear resistance and corrosion resistance of the matrix of the sinteredalloy were improved by the hard phase. When the amount of the hard phaseforming alloy powder was not more than 35%, the wear amount of the valvesheet and the corrosion loss were decreased according to the increase inthe amount of the hard phase forming alloy powder. In the sample No. F10in which the amount of the hard phase forming alloy powder was 45%,compressibility of the raw powder was decreased by the increase in theamount of the hard phase forming alloy powder, whereby the wear amountof the valve sheet and the corrosion loss were slightly increased, butthese were at low levels. On the other hand, in the sample No. F11 inwhich the amount of the hard phase forming alloy powder was greater than45%, the influence of the decrease of compressibility was remarkable,whereby the wear amount of the valve sheet was remarkably increased andthe corrosion loss was increased. Moreover, the wear amount of the valvewas also remarkably increased because the wear particles of the valvesheet eroded the valve. According to the above results, when the amountof the hard phase forming alloy powder (the amount of the hard phasedispersed in the matrix) was 15 to 45%, the wear amounts of the valvesheet and the valve were small.

Example F-3

An iron alloy powder as shown in Table F-3, a graphite powder, and thehard phase forming alloy powder (Co-30% Cr-20% Mo-17% Fe-3% Si powder)used in the sample No. F04 in the example F-1 were prepared. In the ironalloy powder, the amount of Mo was different from that of the iron alloypowder used in the example F-1. The iron alloy powder, 35% of the hardphase forming alloy powder, and 1% of the graphite powder were added andmixed. Furthermore, 0.8 mass parts of zinc stearate as a forminglubricant was added and mixed with 100 mass parts of the mixed powder,and a raw powder was mixed. The obtained raw powder was compacted andsintered in the same way as in the example A-1, and samples Nos. F12 toF16 were formed. The wear tests and the corrosion tests were performedin the same way as in the example C-1 for these samples. The results areshown in Table F-3 with the values of the sample No. F04 in the exampleF-1.

TABLE F-3 Mixing ratio mass % Evaluation item Iron alloy powder Hardphase Wear amount μm Corrosion Sample compositions forming GraphiteValve loss No. Fe Mo alloy powder powder sheet Valve Total mg/cm² NotesF12 Balance Balance 0.00 35.00 1.00 61 4 65 0.25 Comparative example F13Balance Balance 1.00 35.00 1.00 31 5 36 0.16 Practical example F04Balance Balance 3.00 35.00 1.00 18 5 23 0.08 Practical example F14Balance Balance 5.00 35.00 1.00 20 5 25 0.12 Practical example F15Balance Balance 7.00 35.00 1.00 34 6 40 0.15 Practical example F16Balance Balance 8.00 35.00 1.00 56 8 64 0.27 Comparative example

According to Table F-3, the influence of the amount of Mo in the ironalloy powder was investigated. In the sample No. F12 in which the amountof Mo was less than 1%, the wear amount of the valve sheet and thecorrosion loss were large because Fe matrix was not strengthened by Mo.However, in the sample No. F13 in which the amount of Mo in the ironalloy powder was 1%, the wear amount of the valve sheet was remarkablydecreased because the Fe matrix was strengthened by Mo, and thecorrosion loss was decreased because the corrosion resistance of the Fematrix was improved. When the amount of Mo in the iron alloy powder wasnot more than 3%, the wear amount of the valve sheet and the corrosionloss were decreased according to the increase in the amount of Mo in theiron alloy powder. In the samples Nos. F14 and F15 in which the amountof Mo in the iron alloy powder was 5 to 7%, compressibility of the rawpowder was decreased by the increase in the hardness of the iron alloypowder, whereby the density of the green compact was decreased. As aresult, the density of the sintered compact was decreased, whereby thewear amount of valve sheet and the corrosion loss were slightlyincreased, but these were low values. On the other hand, in the sampleNo. F16 in which the amount of Mo in the iron alloy powder was greaterthan 8%, the influence of the increase in the hardness of the iron alloypowder was remarkable, and the density of the sintered compact wasremarkably decreased, whereby the wear amount of the valve sheet and thecorrosion loss were remarkably increased. According to the aboveresults, when the amount of Mo in the iron alloy powder was 1 to 7%, thewear amount of the valve sheet was small and the corrosion loss wasreduced.

Example F-4

The iron alloy powder (Fe-3% Mo powder) used in the example F-1, thehard phase forming alloy powder (Co-30% Cr-20% Mo-17% Fe-3% Si powder)used in the sample No. F04 in the example F-1, and a graphite powderwere prepared. The ratio of the graphite powder was changed as shown inTable F-4, and these powders were added and mixed. Furthermore, 0.8 massparts of zinc stearate as a forming lubricant was added and mixed with100 mass parts of the mixed powder, and a raw powder was obtained. Theobtained raw powder was compacted and sintered in the same way as in theexample A-1, and samples Nos. F17 to F22 were formed. The wear testswere performed in the same way as in the example C-1 for these samples.The results are shown in Table F-4 with the values of the sample No. F04in the example F-1.

TABLE F-4 Mixing ratio mass % Hard phase Evaluation item Sam- Ironforming Wear amount μm ple alloy alloy Graphite Valve No. powder powderpowder sheet Valve Total Notes F17 Balance 35.00 0.30 75 4 79Comparative example F18 Balance 35.00 0.50 42 5 47 Practical example F19Balance 35.00 0.80 21 5 26 Practical example F04 Balance 35.00 1.00 18 523 Practical example F20 Balance 35.00 1.20 2 6 8 Practical example F21Balance 35.00 1.50 41 10 51 Practical example F22 Balance 35.00 1.80 6847 115 Comparative example

According to Table F-4, the influence of the amount of the graphitepowder (the amount of C in the overall composition) was investigated. Inthe sample No. F17 in which the amount of the graphite powder was lessthan 0.5%, the wear amount of the valve sheet was large because Fematrix of the sintered alloy was not sufficiently strengthened. In thesample No. F18 in which the amount of the graphite powder was 0.5%, thewear amount of the valve sheet was remarkably decreased because the Fematrix of the sintered alloy was strengthened. When the amount of thegraphite powder was not more than 1.0%, the wear amount of the valvesheet was decreased according to the increase in the amount of thegraphite powder. In the sample in which the amount of the graphitepowder was 1.2 to 1.5%, the wear amount of the valve sheet was increasedand the wear amount of the valve was slightly increased because the Fematrix of the sintered alloy was hardened and embrittled. In this case,the total of the wear amounts was not a problem in practical use. On theother hand, in the sample No. F22 in which the amount of the graphitepowder was greater than 1.5%, this tendency was more remarkable, andtherefore the wear amount of the valve sheet was remarkably increased.Moreover, the wear amount of the valve was also remarkably increasedbecause the wear particles of the valve sheet eroded the valve.According to the above results, when the amount of the graphite powder(the amount of C in the overall composition) was 0.5 to 1.5%, the wearamounts of the valve sheet and the valve were small.

Example F-5

The iron alloy powder (Fe-3% Mo powder) used in the example F-1, agraphite powder, and a hard phase forming alloy powder as shown in TableF-5 were prepared. The hard phase forming alloy powder had a compositionin which a ratio of Co and Fe was different from that of the hard phaseforming alloy powder (Co-30% Cr-20% Mo-17% Fe-3% Si powder) used in thesample No. F04 in the example F-1. The iron alloy powder, 35% of thehard phase forming alloy powder, and 1% of the graphite powder wereadded and mixed. Furthermore, 0.8 mass parts of zinc stearate as aforming lubricant was added and mixed with 100 mass parts of the mixedpowder, and a raw powder was obtained. The obtained raw powder wascompacted and sintered in the same way as in the example A-1, andsamples Nos. F23 to F28 were formed. The wear tests were performed inthe same way as in the example C-1 for these samples. The results areshown in Table F-5 with the values of the sample No. F04 in the exampleF-1.

TABLE F-5 Mixing ratio mass % Evaluation item Hard phase forming alloypowder Wear amount μm Sample Iron alloy Compositions mass %Subsitutional Graphite Valve No. powder Co Fe Cr Mo Si ratio of Fepowder sheet Valve Total Notes F23 Balance 35.00 Balance 0.00 30.0020.00 3.00 0.00 1.00 14 5 19 Practical example F24 Balance 35.00 Balance0.00 30.00 20.00 3.00 0.00 1.00 16 5 21 Practical example F04 Balance35.00 Balance 0.00 30.00 20.00 3.00 0.00 1.00 18 5 23 Practical exampleF25 Balance 35.00 Balance 0.00 30.00 20.00 3.00 0.00 1.00 20 5 25Practical example F26 Balance 35.00 Balance 0.00 30.00 20.00 3.00 0.001.00 34 6 40 Practical example F27 Balance 35.00 Balance 0.00 30.0020.00 3.00 0.00 1.00 61 7 68 Practical example F28 Balance 35.00 Balance0.00 30.00 20.00 3.00 0.00 1.00 87 16 103 Comparative example

According to Table F-5, when Co in the hard phase forming alloy powderwas substituted by Fe, the influence of the substitutional ratio of Fewas investigated. In the sample No. F23 in which Co in the hard phaseforming alloy powder was not substituted by Fe, the wear amounts werethe lowest among the above examples F and wear resistance was good. WhenCo in the hard phase forming alloy powder was substituted by Fe and thesubstitutional ratio of Fe was increased, the wear amounts wereincreased. In this case, when the substitutional ratio of Fe was notmore than 80% (samples Nos. F04, F24 to F26), the wear amounts were nota problem in practical use. In the samples Nos. F27 and F28 in which thesubstitutional ratio of Fe was more than 80%, the wear amounts wereremarkably increased because the effect of Co was insufficient.According to the above results, although Co in the hard phase formingalloy powder could be substituted by Fe, the substitutional ratio of Feshould be not more than 80%. Furthermore, the substitutional ratio of Fewas preferably not more than 60%.

Example F-6

The iron alloy powder (Fe-3% Mo powder) used in the example F-1, agraphite powder, and a hard phase forming alloy powder as shown in TableF-6 were prepared. The hard phase forming alloy powder was formed byadding different amount of Mn in the hard phase forming alloy powder(Co-30% Cr-20% Mo-17% Fe-3% Si powder) used in the sample No. F04 in theexample F-1. The iron alloy powder, 35% of the hard phase forming alloypowder, and 1% of the graphite powder were added and mixed. Furthermore,0.8 mass parts of zinc stearate as a forming lubricant was added andmixed with 100 mass parts of the mixed powder, and a raw powder wasobtained. The obtained raw powder was compacted and sintered in the sameway as in the example A-1, and samples Nos. F29 to F32 were formed. Thewear tests were performed in the same way as in the example C-1 forthese samples. The results are shown in Table F-6 with the values of thesample No. F04 in the example F-1.

TABLE F-6 Mixing ratio mass % Evaluation item Iron Hard phase formingalloy powder Wear amount μm Sample alloy Compositions mass % GraphiteValve No. powder Co Fe Cr Mo Si Mn powder sheet Valve Total Notes F04Balance 35.00 Balance 17.00 30.00 20.00 3.00 — 1.00 18 5 23 Practicalexample F29 Balance 35.00 Balance 17.00 30.00 20.00 3.00 1.00 1.00 16 521 Practical example F30 Balance 35.00 Balance 17.00 30.00 20.00 3.003.00 1.00 14 7 21 Practical example F31 Balance 35.00 Balance 17.0030.00 20.00 3.00 5.00 1.00 17 13 30 Practical example F32 Balance 35.00Balance 17.00 30.00 20.00 3.00 7.00 1.00 33 51 84 Comparative example

According to Table F-6, the effect of Mn in the hard phase forming alloypowder (the hard phase) was investigated. In the samples Nos. F29 to F31in which the amount of Mn in the hard phase forming alloy powder was notmore than 5%, the alloy matrix of the hard phase was strengthened by Mn,whereby the wear amounts of the valve sheets were less than that of thesample No. F04 in which Mn was not added in the hard phase forming alloypowder. On the other hand, the wear amounts of the valves were slightlyincreased according to the increase in the amount of Mn, because thehard phase was strengthened. In the sample No. F32 in which the amountof Mn in the hard phase forming alloy powder was greater than 5%, thehard phase forming alloy powder was hardened, and compressibility of theraw powder was remarkably decreased, whereby the wear amount of thevalve sheet was remarkably increased. Moreover, the wear amount of thevalve was also remarkably increased because the wear particles of thevalve sheet eroded the valve. According to the above results, althoughwear resistance could be further improved by adding Mn in the hard phaseforming alloy powder, the amount of Mn in the hard phase forming alloypowder should not more than be 5%.

Example F-7

The iron alloy powder (Fe-3% Mo powder) used in the example F-1, thehard phase forming alloy powder (Co-30% Cr-20% Mo-17% Fe-3% Si powder)used in the sample No. F04 in the example F-1, a graphite powder, and anickel powder were prepared. The iron alloy powder, 35% of the hardphase forming alloy powder, 1% of the graphite powder, and a ratio shownin Table F-7 of the nickel powder were added and mixed. Furthermore, 0.8mass parts of zinc stearate as a forming lubricant was added and mixedwith 100 mass parts of the mixed powder, and a raw powder was obtained.The obtained raw powder was compacted and sintered in the same way as inthe example A-1, and samples Nos. F33 to F38 were formed. The wear testswere performed in the same way as in the example C-1 for these samples.The results are shown in Table F-7 with the values of the sample No. F04in the example F-1.

TABLE F-7 Mixing ratio mass % Evaluation item Iron Hard phase Wearamount μm Sample alloy forming alloy Graphite Nickel Valve No. powderpowder powder powder sheet Valve Total Notes F04 Balance 35.00 1.00 0.0018 5 23 Practical example F33 Balance 35.00 1.00 1.00 15 5 20 Practicalexample F34 Balance 35.00 1.00 2.00 14 5 19 Practical example F35Balance 35.00 1.00 3.00 14 5 19 Practical example F36 Balance 35.00 1.004.00 16 6 22 Practical example F37 Balance 35.00 1.00 5.00 18 7 25Practical example F38 Balance 35.00 1.00 7.00 40 10 50 Comparativeexample

According to Table F-7, compared with the sample No. F04 in which thenickel powder was not added to the raw powder and Ni was not added inthe matrix, in the samples Nos. F33 to F37 in which the nickel powderwas added at not more than 5%, the wear amount of the valve sheet wasdecreased and the total of the wear amounts was decreased. In the sampleNo. F38 in which the amount of the nickel powder was greater than 5%, alarge amount of Ni-rich austenite having low wear resistance was formedand remained in the matrix, whereby wear resistance of the valve sheetwas decreased and the wear amount of the valve sheet was increased.Moreover, the amount of hard martensite was increased, and the erosionof the valve (the mating material) was increased, whereby the wearamount of the valve was increased and the total of the wear amounts wasremarkably increased. Accordingly, although wear resistance was improvedby adding the nickel powder, the amount of the nickel powder should benot more than 5.0%.

1. A hard phase forming alloy powder for forming a hard phase dispersedin a sintered alloy, the hard phase forming alloy powder consisting of,by mass %, 15 to 35% of Mo, 1 to 10% of Si, 10 to 40% of Cr, and thebalance of Co and inevitable impurities.
 2. The hard phase forming alloypowder according to claim 1, wherein the amount of Cr is 20 to 40%. 3.The hard phase forming alloy powder according to claim 1, wherein notmore than 80 mass % of Co is substituted by Fe.
 4. The hard phaseforming alloy powder according to claim 1, wherein not more than 5 mass% of Mn is added to the composition.
 5. A production method for a wearresistant sintered alloy, comprising: preparing a matrix forming powder,the hard phase forming alloy powder recited in claim 1, and a graphitepowder; mixing 15 to 45% of the hard phase forming alloy powder and 0.5to 1.5% of the graphite powder with the matrix forming powder into a rawpowder; compacting the raw powder into a green compact having apredetermined shape; and sintering the green compact.
 6. The productionmethod for the wear resistant sintered alloy according to claim 5,wherein the matrix forming powder is a mixed powder consisting of 1 to 5mass % of a nickel powder and the balance of an iron powder.
 7. Theproduction method for the wear resistant sintered alloy according toclaim 6, wherein the iron powder is an ore-reduced iron powder including0.3 to 1.5 mass % of metallic oxides.
 8. The production method for thewear resistant sintered alloy according to claim 5, wherein the matrixforming powder is an iron alloy powder consisting of 1 to 5 mass % of Crand the balance of Fe and inevitable impurities.
 9. The productionmethod for the wear resistant sintered alloy according to claim 8,wherein the iron alloy powder further includes at least one of Mo, V,and Nb at not more than 2.4 mass %.
 10. The production method for thewear resistant sintered alloy according to claim 5, the matrix formingpowder is a mixed powder consisting of an iron alloy powder and not morethan 5 mass % of a nickel powder with respect to the raw powder, and theiron alloy powder consists of 1 to 5 mass % of Cr and the balance of Feand inevitable impurities.
 11. The production method for the wearresistant sintered alloy according to claim 5, wherein the matrixforming powder is an iron alloy powder consisting of, by mass %, 3 to 8%of Co, 1 to 2% of Ni, 1 to 2% of Mo, and the balance of Fe andinevitable impurities.
 12. The production method for the wear resistantsintered alloy according to claim 5, wherein the matrix forming powderis a mixed powder consisting of an iron alloy powder and not more than 5mass % of a nickel powder with respect to the raw powder, and the ironalloy powder consists of, by mass %, 3 to 8% of Co, 1 to 2% of Ni, 1 to2% of Mo, and the balance of Fe and inevitable impurities.
 13. Theproduction method for the wear resistant sintered alloy according toclaim 5, wherein the matrix forming powder is an iron alloy powderconsisting of, by mass %, 1 to 3% of Ni, 0.5 to 2% of Mo, 0.1 to 1% ofCr, 0.1 to 0.5% of Mn, and the balance of Fe and inevitable impurities.14. The production method for the wear resistant sintered alloyaccording to claim 5, wherein the matrix forming powder is a mixedpowder consisting of an iron alloy powder and not more than 5 mass % ofat least one of a nickel powder and a copper powder with respect to theraw powder, and the iron alloy powder consists of, by mass %, 1 to 3% ofNi, 0.5 to 2% of Mo, 0.1 to 1% of Cr, 0.1 to 0.5% of Mn, and the balanceof Fe and inevitable impurities.
 15. The production method for the wearresistant sintered alloy according to claim 5, wherein the matrixforming powder is an iron alloy powder consisting of 1 to 7 mass % of Moand the balance of Fe and inevitable impurities.
 16. The productionmethod for the wear resistant sintered alloy according to claim 5,wherein the matrix forming powder is a mixed powder consisting of aniron alloy powder and not more than 5 mass % of a nickel powder withrespect to the raw powder, and the iron alloy powder consists of 1 to 7mass % of Mo and the balance of Fe and inevitable impurities.
 17. Theproduction method for the wear resistant sintered alloy according toclaim 5, wherein the raw powder further includes at least one kind ofpowder of machinability improving material at 0.3 to 2 mass %, and thepowder of the machinability improving material is selected from thegroup consisting of a lead powder, a disulfide molybdenum powder, amanganese sulfide powder, a boron nitride powder, a calcium metasilicatemineral powder, and a calcium fluoride powder.
 18. The production methodfor the wear resistant sintered alloy according to claim 5, wherein thewear resistant sintered alloy obtained by sintering has pores, and theproduction method further comprising infiltrating or impregnating thepores with one selected from the group consisting of lead, lead alloy,copper, copper alloy, and acrylic resin.
 19. A wear resistant sinteredalloy exhibiting a metallic structure in which 15 to 45% of a hard phaseis dispersed in a matrix, the hard phase consisting of, by mass %, 15 to35% of Mo, I to 10% of Si, 10 to 40% of Cr, and the balance of Co andinevitable impurities.
 20. The wear resistant sintered alloy accordingto claim 19, wherein not more than 80 mass % of Co is substituted by Fein the composition of the hard phase.
 21. The wear resistant sinteredalloy according to claim 19, wherein the hard phase further includes notmore than 5 mass % of Mn.
 22. The wear resistant sintered alloyaccording to claim 19, wherein the wear resistant sintered alloy has anoverall composition consisting of, by mass %, 1 to 5% of Ni, 2.25 to33.3% of Co, 1.5 to 18% of Cr, 2.25 to 15.75% of Mo, 0.15 to 4.5% of Si,0.5 to 1.5% of C, and the balance of Fe and inevitable impurities, andthe matrix is made of an Fe—Ni—C alloy.
 23. The wear resistant sinteredalloy according to claim 22, wherein the matrix of the Fe—Ni—C alloyincludes at least one kind of an oxide of a metal at 0.15 to 1.25 mass %with respect to the overall composition, and the metal is selected fromthe group consisting of aluminum, silicon, magnesium, iron, titanium,and calcium.
 24. The wear resistant sintered alloy according to claim19, wherein the wear resistant sintered alloy has an overall compositionconsisting of, by mass %, 2.34 to 20.73% of Cr, 2.25 to 15.75% of Mo,0.15 to 4.5% of Si, 2.25 to 33.3% of Co, 0.5 to 1.5% of C, and thebalance of Fe and inevitable impurities, and the matrix is made of anFe—Cr—C alloy.
 25. The wear resistant sintered alloy according to claim24, wherein the matrix of the Fe—Cr—C alloy further includes at leastone of Mo, V, and Nb at not more than 2 mass % with respect to theoverall composition.
 26. The wear resistant sintered alloy according toclaim 24, wherein the matrix of the Fe—Cr—C alloy further includes Ni atnot more than 5 mass % with respect to the overall composition.
 27. Thewear resistant sintered alloy according to claim 19, wherein the wearresistant sintered alloy has an overall composition consisting of, bymass %, 1.5 to 18% of Cr, 0.54 to 1.69% of Ni, 3.09 to 16.84% of Mo,0.15 to 4.5% of Si, 4.76 to 37.66% of Co, 0.5 to 1.5% of C, and thebalance of Fe and inevitable impurities, and the matrix is made of anFe—Co—C alloy.
 28. The wear resistant sintered alloy according to claim27, wherein the matrix of the Fe—Co—C alloy further includes Ni at notmore than 5 mass % with respect to the overall composition.
 29. The wearresistant sintered alloy according to claim 19, wherein the wearresistant sintered alloy has an overall composition consisting of, bymass %, 1.58 to 18.55% of Cr, 0.54 to 2.54% of Ni, 2.67 to 16.84% of Mo,0.15 to 4.5% of Si, 2.25 to 33.30% of Co, 0.05 to 0.42% of Mn, 0.5 to1.5% of C, and the balance of Fe and inevitable impurities, and thematrix is made of an Fe—Ni—Mo—C alloy.
 30. The wear resistant sinteredalloy according to claim 29, wherein the matrix of the Fe—Ni—Mo—C alloyfurther includes at least one of Ni and Cu at not more than 5.0 mass %with respect to the overall composition.
 31. The wear resistant sinteredalloy according to claim 19, wherein the wear resistant sintered alloyhas an overall composition consisting of, by mass %, 1.5 to 18% of Cr,3.09 to 19.57% of Mo, 0.15 to 4.5% of Si, 2.25 to 33.3% of Co, 0.5 to1.5% of C, and the balance of Fe and inevitable impurities, and thematrix is made of an Fe—Mo—C alloy.
 32. The wear resistant sinteredalloy according to claim 31, wherein the matrix of the Fe—Mo—C alloyfurther includes Ni at not more than 5.0 mass % with respect to theoverall composition.
 33. The wear resistant sintered alloy according toclaim 19, wherein the sintered alloy has pores and grain boundaries, atleast one kind of powder of machinability improving material isdispersed in the pores and the grain boundaries at 0.3 to 2 mass %, andthe machinability improving material is selected from the groupconsisting of lead, disulfide molybdenum, manganese sulfide, boronnitride, calcium metasilicate mineral, and calcium fluoride.
 34. Thewear resistant sintered alloy according to claim 19, wherein thesintered alloy has pores filled with one kind selected from the groupconsisting of lead, lead alloy, copper, copper alloy, and acrylic resin.